FEDERAL ENERGY MANAGEMENT PROGRAM

Application Domain

The potential for cost-effective application of cool storage systems of one type or

another exists in most buildings with a space

cooling system. Originally, cool storage technology was developed for integration with chilled

water cooling systems that typically serve larger

buildings. More recent cool storage developments have included technologies designed for

integration with roof-mounted, direct-expansion

(DX) cooling systems. Residential-sized cool

storage technologies, including smaller versions

of the equipment designed for the roof-mounted

DX application, have also been developed, but

cost economies-of-scale have been difficult to

overcome in the residential market.

Although originally developed to shift electrical

demand to off-peak periods (from an electric

utility’s perspective) and to take advantage of

low-cost off-peak electric rates (from an enduser’s perspective), many applications can also

result in lower first costs and/or higher system

efficiency compared to non-storage systems.

Therefore, while a large differential between

on-peak and off-peak kWh charges or a high

demand charge definitely improves cool storage

economics, cost-effective applications also exist

without these benefits. Still, not every

cooling system presents a cost-effective

application, so careful consideration of

site-specific conditions is warranted to

determine whether

cool storage makes

sense or not, which

cool storage technology is best, and the

optimum configuration for a specific

technology.

Thermal Energy Storage for Space Cooling

Technology for reducing on-peak electricity demand and cost

Internet: http://www.eren.doe.gov/femp

Federal

Technology

Alert

A publication series

designed to speed the

adoption of energyefficient and renewable

technologies in the

Federal sector

Prepared by the

New Technology

Demonstration

Program

DOE/EE-0241

No portion of this publication may be altered

in any form without prior

written consent from the

U.S. Department of Energy

and the authoring national

laboratory.

Thermal energy storage for space cooling, also

known as cool storage, chill storage, or cool thermal storage, is a relatively mature technology

that continues to improve through evolutionary

design advances. Cool storage technology can

be used to significantly reduce energy costs by

allowing energy-intensive, electrically driven

cooling equipment to be predominantly operated during off-peak hours when electricity rates

are lower. In addition, some system configurations

result in lower first costs and/or lower operating

costs compared to non-storage systems.

A survey of approximately 25 manufacturers

providing cool storage systems or components

identified several thousand current installations,

but less than 1% of these were at Federal facilities. With the Federal sector representing nearly

4% of commercial building floor space and 5% of

commercial building energy use, Federal utilization would appear to be lagging. The potential

cost savings resulting from the application of

cool storage systems in the Federal sector is estimated to be $50 million per year. Thus, this

Federal Technology Alert has been written to reintroduce the concept and make Federal energy

managers aware of the latest technologies and

energy- and cost-saving opportunities.

Modular ice-on-coil storage tanks with condenser units above

Photo courtesy of Calmac Manufacturing Corporation
Design Variations

There are many different types of cool

storage systems representing different

combinations of storage media, charging

mechanisms, and discharging mechanisms. The basic media options are water,

ice, and eutectic salts. Ice systems can be

further broken down into ice harvesting,

ice-on-coil, ice slurry, and encapsulated

ice options. Ice-on-coil systems may be

internal-melt or external-melt and may

be charged and discharged with refrigerant or a single-phase coolant (typically

a water/glycol mixture). Independent

of the technology choice, cool storage

systems can be designed to provide

full storage or partial storage, with loadleveling and demand-limiting options for

partial storage. Finally, storage systems

can be operated on a chiller-priority or

storage-priority basis whenever the cooling load is less than the design conditions.

Chilled water storage systems rely solely

on the sensible (i.e., no phase change or

latent energy) heat capacity of water

and the temperature difference between

supply and return water streams going

to and from the cooling load. Ice-on-coil

systems come in several variations, as

noted above. In all variations, ice is

formed on a heat transfer surface (generically referred to as a “coil,” whatever the

actual configuration or material) without being released during the charging

mode and melted away during the discharge mode. Ice-harvesting systems

form ice on coils or other refrigerant

evaporating surfaces and periodically

release the ice into a storage tank that

contains a mixture of ice and water. Ice

slurry systems produce small particles

of ice within a solution of glycol and

water, resulting in a slushy mixture that

FEDERAL ENERGY MANAGEMENT PROGRAM

Disclaimer

This report was sponsored by the United States Department of Energy, Office of Federal Energy Management

Programs. Neither the United States Government nor any agency or contractor thereof, nor any of their employees,

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not

infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade

name, mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency or contractor thereof. The views and opinions of

authors expressed herein do not necessarily state or reflect those of the United States Government or any agency or

contractor thereof.

can be pumped. Encapsulated ice systems consist of water contained in plastic containers surrounded by coolant, all

contained within a tank or other storage

vessel. Eutectic salt systems are similar

to encapsulated ice systems, but the

plastic enclosures contain a eutectic salt

instead of water.

Full storage systems are designed to

meet all on-peak cooling loads from

storage. Partial storage systems meet

part of the cooling load from storage and

part directly from the chiller during the

on-peak period. Load-leveling partial

storage is designed for the chiller to

operate at full capacity for 24 hours on

the peak demand day. Demand limiting partial storage represents a middle

ground between full storage and loadleveling partial storage where chiller

operation is reduced but not eliminated

during the on-peak period. Storage priority and chiller priority are two alternative operating strategies for cool storage

systems with partial storage designs. As

the names imply, cooling is preferentially

provided from storage with storage priority operation and directly from the

chiller with chiller priority operation.

Where to Apply

Cool storage will reduce the average

cost of energy consumed and can potentially reduce the energy consumption

and initial capital cost of a cooling system

compared to a conventional cooling system without cool storage. While most

building space cooling applications are

potentially attractive candidates, the

prospects will be especially attractive

if one or more of the following conditions exists.

• Electricity energy charges vary significantly during the course of a day.

• Electricity demand charges are high

or ratcheted.

• The average cooling load is significantly less than the peak cooling load.

• The electric utility offers other incentives (besides the rate structure) for

installing cool storage.

• An existing cooling system is expanded.

• There is new construction.

• Older cooling equipment needs

replacing.

• Cold air distribution benefits can be

captured.

What to Avoid

In general, applications lacking the

conditions identified above should be

avoided. In addition, the following

conditions should also be avoided.

• Lack of operation and maintenance

experience or training with system

equipment, especially where built-up

refrigeration systems are used rather

than packaged chillers.

• Lack of operator training on operating and control strategies for minimizing cooling system life-cycle costs.

• Sites where the space available for

cool storage equipment is limited

or has other, more valuable uses.

• Limited resources for engineering

feasibility studies and system design.

Cool storage systems are inherently

more complicated than non-storage

systems and extra time will be

required to determine the optimum

system for a given application.
There are many different

types of cool storage systems representing different

combinations of storage

media, charging mechanisms, and discharging

mechanisms. The basic

media options are water,

ice, and eutectic salts. Ice

systems can be further

broken down into ice harvesting, ice-on-coil, ice

slurry, and encapsulated

ice options. Ice-on-coil systems may be internal melt

or external melt and may

be charged and discharged

with refrigerant or a single-phase coolant (typically a water/glycol mixture). Independent of

the technology choice, cool storage systems can

be designed to provide full storage or partial

storage, with load-leveling and demand-limiting

options for partial storage. Finally, storage systems

can be operated on a chiller-priority or storagepriority basis whenever the cooling load is less

than the design conditions.

The first section describes the basic types of cool

storage technologies and cooling system integration options. The next three sections define the

savings potential in the Federal sector, present

application advice, and describe the performance

experience of specific Federal users. A step-by-step

methodology illustrating how to evaluate cool

storage options is presented next, followed by a

case study of a GSA building using cool storage.

Latter sections list manufacturers, selected Federal

users, and reference materials. Finally, the appendixes give Federal life-cycle costing procedures

and results for a case study.

Thermal Energy Storage for Space Cooling

Technology for reducing on-peak electricity demand and cost

Federal

Technology

Alert

1

FEDERAL ENERGY MANAGEMENT PROGRAM

A stratified chilled water storage tank with cooling towers on the left

Abstract

Cool storage technology can be used to significantly reduce energy costs by allowing energyintensive, electrically driven cooling equipment

to be predominantly operated during off-peak

hours when electricity rates are lower. In addition, some system configurations may result in

lower first costs and/or lower operating costs.

Cool storage systems of one type or another

could potentially be cost-effectively applied in

most buildings with a space cooling system. A

survey of approximately 25 manufacturers providing cool storage systems or components identified several thousand current installations, but

less than 1% of these were at Federal facilities.

With the Federal sector representing nearly 4% of

commercial building floor space and 5% of commercial building energy use, Federal utilization

would appear to be lagging. Although current

applications are relatively few, the estimated

potential annual savings from using cool storage

in the Federal sector is $50 million.

Photo courtesy of Pitt-DesMoines, Inc.
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FEDERAL ENERGY MANAGEMENT PROGRAM

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FEDERAL ENERGY MANAGEMENT PROGRAM

Contents

Abstract ........................................................................................................................... 1

About the Technology .................................................................................................... 5

Application Domain

Energy-Saving Mechanism

Cold Air Distribution

Other Benefits

Variations: Storage Media and Mechanisms

Variations: Design and Operating Strategies

Installation

Federal Sector Potential .................................................................................................. 12

Estimated Savings and Market Potential

Laboratory Perspective

Application ..................................................................................................................... 13

Application Screening

Where to Apply

What to Avoid

Equipment Integration

Maintenance Impact

Equipment Warranties

Costs

Utility Incentives and Support

Technology Performance ................................................................................................ 16

Evaluating Cool Storage Systems .................................................................................. 17

Cooling Requirements

Identifying Alternatives

Screening Alternatives

Refining the Evaluation

Case Study ...................................................................................................................... 22

Facility Description

Existing Technology Description

New Technology Equipment Selection

Savings Potential

Life-Cycle Cost

Implementation and Post-Implementation Experience

The Technology in Perspective ....................................................................................... 23

The Technology’s Development

Technology Outlook

Manufacturers ................................................................................................................ 24

Who is Using the Technology......................................................................................... 25

For Further Information ................................................................................................. 26

Associations

Design and Installation Guides

References ....................................................................................................................... 26

Appendix A: Federal Life-Cycle Costing Procedures and the BLCC

Software ................................................................................................ 31

Appendix B: QuickBLCC Results for Case Study .................................................... 32
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FEDERAL ENERGY MANAGEMENT PROGRAM

About the Technology

Thermal energy storage for space cooling, also known as cool storage, chill

storage, or cool thermal storage, is a relatively mature technology that continues

to improve through evolutionary design

advances. Cool storage technology can

be used to significantly reduce energy

costs by allowing energy-intensive,

electrically driven cooling equipment

to be predominantly operated during

off-peak hours when electricity rates

are lower. In addition, some system

configurations result in lower first costs

and/or lower operating costs. Unfortunately, cool storage technologies have

been underutilized in the Federal sector

compared to the private sector. Thus,

this Federal Technology Alert has been

written to reintroduce the concept and

make Federal energy managers aware

of the latest technologies and energyand cost-saving opportunities.

Cool storage technologies come in many

different forms, each with their pros and

cons. The storage media is most commonly water (with “cold” stored in the

form of ice, chilled water, or an ice/water

slurry), but other media (most notably

eutectic salts) have also been used. Storage media can be cooled (charged) by

evaporating refrigerant or a secondary

coolant (typically a water/glycol mixture). Discharge is usually accomplished

directly via circulating water or indirectly

via secondary coolant. At least one system has been developed that discharges

storage via circulating refrigerant.

Application Domain

Cool storage systems of one type or another could potentially be cost-effectively

applied in most buildings with a space

cooling system. Originally, cool storage

technology was developed for integration with chilled water cooling systems

that typically serve larger buildings.

More recent cool storage developments

have included technologies designed for

integration with roof-mounted, directexpansion (DX) cooling systems. Residential-sized cool storage technologies,

including smaller versions of the equipment designed for the roof-mounted DX

application, have also been developed,

but cost economies-of-scale have been

difficult to overcome in the residential

market.

Although originally developed to shift

electrical demand to off-peak periods

(from an electric utility’s perspective)

and to take advantage of low-cost offpeak electric rates (from an end-user’s

perspective), many applications can

also result in lower first costs and/or

higher system efficiency compared to

non-storage systems. Therefore, while

a large differential between on-peak

and off-peak kWh charges or a high

demand charge definitely improves

cool storage economics, cost-effective

applications also exist without these

benefits. Still, not every cooling system

presents a cost-effective application, so

careful consideration of site-specific

conditions is warranted to determine

whether cool storage makes sense or

not, which cool storage technology is

best, and the optimum configuration

for a specific technology.

A survey of approximately 25 manufacturers providing cool storage systems or

components identified several thousand

current installations, but less than 1% of

these were at Federal facilities. With

the Federal sector representing nearly

4% of commercial building floor space

and 5% of commercial building energy

use, Federal utilization would appear

to be lagging.

Energy-Saving Mechanism

Cool storage systems are not commonly

thought of as energy-saving technologies. No matter how well insulated,

thermal storage systems inevitably suffer some losses as energy flows from

warmer bodies to cooler bodies. In addition, both cool and warm water is commonly stored in the same storage tank

in chilled water systems to save on tank

costs. Mixing is minimized by injecting

and removing water from different halves

of the tank via specially designed piping

to take advantage of natural differences

in water density and buoyancy at different temperatures. Still, some mixing and

loss of cooling capability are inevitable.

Historically, the driving force for developing cool storage has been reduction of

on-peak electric demand and the corresponding reduction of electricity costs.

While this is still important, and may

be the most important factor affecting

application cost-effectiveness, energy

savings are possible, and can be a significant benefit when the entire cooling

system, and not just the storage media

and vessel are considered.

Besides heat gain by the storage media,

chillers in cool storage systems operate

at lower evaporator temperatures, which

increases energy consumption if other

conditions remain the same. This is

particularly true for ice storage systems,

which require the lowest evaporator

temperatures. The impact of lower

evaporator temperatures is partially or

totally offset, however, by the lower condensing temperatures generally experienced when operating a chiller at night

rather than during the day. In most parts

of the country, dry-bulb temperatures

are about 20°F lower and wet-bulb temperatures 5°F lower at night than during

the day (MacCracken 1993). Thus, nighttime operation improves the efficiency

of all chillers, but especially improves

the efficiency of air-cooled chillers, where

the condensing temperature is controlled

by ambient dry-bulb temperature. Chiller

efficiency is also improved with storage

by allowing more continuous operation

at outputs closer to full capacity, thus

minimizing part-load losses. In retrofit

situations, adding storage to meet peak

cooling demands allows the least efficient chillers to be left off or run much

less, further increasing savings.

Cool storage systems, with separate

charge and discharge cycles, will generally require more pumping. This potential disadvantage can be minimized,

however, by increasing the difference

between water supply and return temperature by a few degrees, thus reducing
6

FEDERAL ENERGY MANAGEMENT PROGRAM

the volume of water that must be circulated. Pumping energy may also be

minimized with variable-speed drives.

The energy savings possible with cool

storage will vary significantly from site

to site, depending on the load profile

and the specific cooling system equipment employed. For example, Caldwell

and Bahnbleth (1997) reported energy

savings ranging from 1–27% for cooling

systems with chilled water storage,

depending on the load profile. Additional discussion of the energy impacts

of cool storage can be found in Bahnbleth

and Joyce (1995), Strutz (1995), and

Duffy (1992).

Cold Air Distribution

Ice storage systems also present an

opportunity for energy savings via

cold air distribution. The supply of

near-freezing water to air-handling

units allows return air to be cooled to

a lower temperature. Primary air is

distributed at 45°F in a cold air system

compared to 55°F in a conventional

system, which allows air flow to be

reduced by about 40% (ASHRAE 1993).

The colder primary air is fully mixed

with a portion of the return air to achieve

the desired room delivery temperature.

Thus, smaller, less costly air handlers

and ducting may be installed, with proportional reductions in fan power consumption. Where growing cooling loads

have exceeded the capacity of existing

air distribution systems, cold air distribution could be implemented to increase

capacity without significant renovation

to the ducting and air-handling system.

Cooling the primary air to 45°F will

also lower conditioned space relative

humidity from 60% to 35%, which generally improves the perceived comfort

of occupants. This effect may allow a

3°F increase in the dry-bulb temperature

set point with the same perceived comfort (MacCracken 1994).

Reducing the size of air-handling equipment lowers construction costs for multistory buildings by reducing the height

system. Included here are costs associated with refrigerant replacement and

cooling tower cleaning and water treatment (ASHRAE 1993).

Variations: Storage Media

and Mechanisms

There are many different types of cool

storage systems representing different

combinations of storage media, charging mechanism, and discharging mechanism. The basic media options are water,

ice, and eutectic salts. Ice systems can be

further broken down into ice harvesting,

ice-on-coil, ice slurry, and encapsulated

ice options. Ice-on-coil systems may be

internal melt or external melt and may

be charged and discharged with refrigerant or a single-phase coolant (typically

a water/glycol mixture). Independent of

the technology choice, cool storage systems can be designed to provide full storage or partial storage, with load-leveling

and demand-limiting options for partial

storage. Finally, storage systems can be

operated on a chiller-priority or storagepriority basis whenever the cooling load

is less than the design conditions.

Chilled water storage systems rely solely

on the sensible (i.e., no phase change or

latent energy) heat capacity of water

and the temperature difference between

supply and return water streams going

to and from the cooling load. As a result,

the storage volume required is greater

than for any of the ice or eutectic salt

options. However, using water eliminates the need for secondary coolants

and heat exchangers and standard water

chillers can be used without significantly degraded performance or capacity. Water is typically cooled to between

39 and 44°F, or slightly lower than for a

standard chilled water system without

storage. The return water temperature

may be increased slightly as well, but

must remain low enough to ensure

adequate indoor humidity control.

Maximizing the difference between cooling water supply and return temperatures maximizes the sensible energy

storage capacity per unit of water and

required per floor for HVAC systems.

The cumulative height savings allowed

the installation of an extra floor within

the same total building height at a

high-rise office building in Bellevue,

Washington (Hasnain 1998).

Early problems with cold air distribution

included fan-powered mixing boxes

that negated much of the energy savings,

poor air diffusers that created comfort

problems, and condensation problems

on some surfaces. Improved designs

have essentially eliminated the former

two problems and condensation problems can be minimized by locating ducts

in air-conditioned space. A bibliography

of references describing cold air distribution is presented in the Design Guide

for Cool Thermal Storage (ASHRAE 1993).

Other Benefits

In addition to reducing the average cost

of electricity consumed and possibly

reducing energy consumption, cool

storage can reduce overall cooling system capital and maintenance costs. For

new construction, partial storage designs

(where the chiller and storage combine

to meet peak cooling loads) reduce chiller

(and cooling tower and cooling water

piping for water-cooled chillers) capacity and cost. Savings in chiller and related

costs are often greater than the incremental costs of the partial storage unit.

Similarly, adding storage is a way to

increase a cooling system’s peak capacity without adding new chillers in situations where cooling load is growing.

Retrofit of old rooftop air-conditioning

systems with cool storage systems can

also be less expensive than replacement

with new rooftop units. Placement of

the cool storage system on the ground

avoids expensive crane or helicopter

charges associated with replacing the

old rooftop unit, which is left in place

and modified slightly to work with the

storage system. Rooftop replacements

may also require structural modifications which can be expensive. Finally,

maintenance costs will be less for the

down-sized components of the storage
7

FEDERAL ENERGY MANAGEMENT PROGRAM

minimizes the size of the storage tank.

A single tank is usually used to store

both the chilled water and the warm

water returning from the cooling load.

Separation of the two water bodies is

maximized by placing the cooler, denser

water at the bottom of the tank and the

warmer water at the top of the tank.

Specially designed piping networks

called diffusers allow water to enter and

leave the tank without causing significant mixing. The result is a layer of cold

water separated from a layer of warm

water by a thermocline, as shown in

Figure 1. Chilled water systems tend to

work best in retrofit situations (no chiller

modifications required) and/or higher

capacity systems where size economiesof-scale lower the unit cost of the tank.

A typical chilled water storage system

configuration is shown in Figure 2.

Chilled water storage tanks may also

be used as a reservoir for fire-protection

water, reducing total facility costs and/

or fire insurance premiums.

Ice-harvesting systems form ice on coils

or other refrigerant evaporating surfaces

and periodically release the ice into a

storage tank that contains a mixture of

ice and water. A typical ice harvesting

storage system configuration is shown

in Figure 3. Water is pumped from the

bottom of the tank and passed over the

refrigerant evaporating surface during

the charging cycle. During discharge,

water is pumped from the tank to the

load. Warm water returns from the load

and is sprayed onto the top of the ice

water mixture to facilitate mixing and

heat transfer between ice and water.

Compared to ice-on-coil systems, ice

harvesters have much less ice-making

surface, but the surface is a specialized

design to facilitate ice release, so the

potential cost savings is not as great as

a comparison based on area would suggest. The average thickness of ice on the

heat transfer surface is generally less,

however, which improves performance.

Figure 2. Typical chilled water configuration.(a)

Figure 1. Chilled water stratification.(a)

On the other hand, ice harvesters must

go through a defrost cycle to release ice

from the heat transfer surface, which

results in a significant performance

penalty. Ice harvesting refrigeration

equipment tends to be more expensive

(a) Copyright 1994, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. www.ashrae.org. Reprinted by permission from Design Guide for Cool Thermal Storage.
8

FEDERAL ENERGY MANAGEMENT PROGRAM

than other cool storage options while

the storage capacity itself is generally

the least expensive. Thus, ice-harvesting

systems are most attractive for applications requiring high storage capacity

and relatively low refrigeration capacity.

Ice-on-coil systems come in several

variations, as noted above. In all variations, ice is formed on a heat transfer

surface (generically referred to as a

“coil,” whatever the actual configuration or material) without being released

during the charging mode and melted

away during the discharge mode. Coils

are packed in various arrangements

within a tank and surrounded by water.

Ice is formed by transferring energy

from the water to an evaporating refrigerant or secondary coolant (generally a

glycol/water mixture) passing through

the coils. Discharge is accomplished by

circulating warm water past the outside of the ice on external-melt systems

while secondary coolant is usually past

through the coils on internal-melt systems. Charging and discharging of

external-melt and internal-melt systems

are illustrated in Figures 4 and 5. At least

one internal-melt system designed for

retrofit of direct-expansion rooftop cooling equipment is discharged by condensing a refrigerant, but this is an exception

to the general use of a secondary coolant.

Some external-melt systems bubble air

though the water to facilitate uniform

freezing and melting of ice. This is not

required on internal-melt systems that

are frozen solid. Freezing all of the water

also results in slightly higher chill storage density for the internal-melt design.

External-melt systems are able to avoid

using a secondary coolant and coolant/

water heat exchangers and also benefit

from direct-contact heat exchange. However, if not fully discharged, remaining

ice on the coil will result in an efficiency

penalty during the subsequent charging

cycle. Care must also be taken to avoid Figure 3. Typical ice-harvesting configuration.(b)

Figure 4. External-melt ice-on-coil.(b)

Figure 5. Internal-melt ice-on-coil.(b)

(b) Copyright 1994, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. www.ashrae.org. Reprinted by permission from Design Guide for Cool Thermal Storage.
9

FEDERAL ENERGY MANAGEMENT PROGRAM

overcharging the external-melt storage

unit solid as it will become increasingly

difficult to discharge without adequate

water flow passages. Charging with

refrigerant is more efficient than with a

secondary coolant because one less heat

transfer step is involved. On the other

hand, charging with a secondary coolant uses much less refrigerant and the

refrigeration system is generally less

complicated. Typical ice-on-coil system

configurations are shown in Figures 6,

7, and 8.

Ice slurry systems produce small particles of ice within a solution of glycol

and water, resulting in a slushy mixture

that can be pumped. Like ice harvesters,

ice slurry generators are dynamic icemaking machines, in contrast to the

static ice-on-coil systems. Thus, ice

slurry generators do not suffer from the

efficiency degradation that occurs as

ice builds up on an evaporator surface.

However, unlike ice harvesters, no

defrost cycle is required for ice slurry

generators, which avoids another efficiency loss. In ice slurry systems, ice particles are generated by passing a weak

glycol/water solution (~ 5-10% glycol)

through tubing that is surrounded by

an evaporating refrigerant contained

within a shell (i.e., the evaporator unit

is a shell-and-tube heat exchanger). As

the glycol/water solution is cooled by

the evaporating refrigerant, ice particles

form. Depending on the system configuration, the resulting slush can either

drop directly into a storage tank or be

pumped into a storage tank. The latter

configuration is illustrated in Figure 9.

Ice-free glycol/water solution is pumped

from the storage tank. Discharge is

accomplished by pumping the cool

solution from the tank either directly

through the cooling load or through

an intermediate heat exchanger that isolates the cooling load from the ice slurry

system. Warm solution is returned to the

top of the tank and distributed over the

ice slurry via multiple spray nozzles.

Figure 6. Direct refrigerant external-melt ice-on-coil configuration.(c)

Figure 7. Secondary coolant external-melt ice-on-coil configuration.(c)

(c) Copyright 1994, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. www.ashrae.org. Reprinted by permission from Design Guide for Cool Thermal Storage.
10

FEDERAL ENERGY MANAGEMENT PROGRAM

Figure 9. Typical ice slurry configuration. Figure 8. Typical internal-melt ice-on-coil (d)

configuration.(d)

Figure 10. Encapsulated ice balls.(d)

Figure 11. Typical encapsulated ice

configuration.(d)

The small size of the particles results in

better heat transfer between the solution

and the ice than is possible for either ice

harvesting or ice-on-coil systems. Like an

ice harvester, ice slurry systems have relatively high fixed costs associated with

the evaporator or ice generator component, but relatively low incremental costs

as storage capacity is added. Thus, ice

slurry systems will look their best in relatively high storage capacity applications.

Encapsulated ice systems consist of

water contained in plastic containers

surrounded by coolant, all contained

within a tank or other storage vessel.

During the charging cycle subfreezing

coolant from a chiller is circulated

through the storage tank and past the

plastic containers, freezing the ice. Discharge is accomplished by circulating

warm coolant through the tank and past

the containers, melting the ice. These two

processes are shown in Figure 10. The

coolant may be routed directly to the

load or be isolated from the load via

a heat exchanger. The most common

form of plastic container is a dimpled

ball about 4 inches in diameter. The

spherical shape creates a relatively

high heat transfer area per unit of water

being frozen, while the dimples allow

for expansion and contraction while

cycling between liquid and solid states.

Either atmospheric or pressurized storage tanks can be used, but a screen must

be used near the top of an atmospheric

tank to keep the balls below the coolant

level. Installation is relatively simple;

the balls are simply poured into a tank

and naturally conform to whatever

shape the storage vessel may be. A typical encapsulated ice system configuration is shown in Figure 11.

Eutectic salt systems are similar to

encapsulated ice systems, but the plastic

enclosures contain a eutectic salt instead

of water. One type of stacked eutectic

salt containers is shown in Figure 12.

Eutectic salts made for cool storage

applications are typically a combination of inorganic salts, water, and nucleating and stabilizing agents that freeze

(d) Copyright 1994, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. www.ashrae.org. Reprinted by permission from Design Guide for Cool Thermal Storage.
11

FEDERAL ENERGY MANAGEMENT PROGRAM

at 47°F and have a latent heat of 41 Btu

per pound (E Source 1998). This compares to a latent heat of 144 Btu per

pound for water. Eutectic salt systems

offer higher energy density than chilled

water systems and like chilled water

systems can be charged with standard

chillers without the efficiency penalty

of a lower evaporator temperature. The

eutectic salts are more expensive than

water, of course. In addition, the water

temperature leaving a eutectic salt system during discharge will be warmer

than normally supplied to a cooling load.

This will generally require downstream

operation of a chiller (see Figure 13) to

larger and, therefore, more expensive

chiller and storage units compared to

partial storage systems. However, full

storage also captures the greatest savings possible by shifting electricity

demand from on-peak to off-peak. Full

storage systems are relatively attractive

when demand charges are high, the differential between on-peak and off-peak

energy charges is high and/or when the

peak demand period is short.

Load leveling and demand limiting

versions of partial storage systems are

also illustrated in Figure 14. In general,

partial storage systems meet part of

the cooling load from storage and part

directly from the chiller during the

on-peak period. Load leveling versions

are designed for the chiller to operate

at full capacity for 24 hours on the peak

demand day. Storage is charged when

the load is less than the output of the

chiller and discharged when the load is

greater than the output of the chiller.

Load leveling designs minimize the size

and cost of chiller and storage components, but achieve less electricity cost

savings than full storage systems. Load

leveling systems are relatively attractive

when electric rate incentives for load

shifting are moderate, the ratio of peak

to average load is high, and/or the

on-peak period is long. Demand limiting partial storage represents a middle

ground between full storage and load

leveling partial storage where chiller

operation is reduced, but not eliminated

during the on-peak period. Thus, system

size and cost, and electricity cost savings

tend to fall between that for the other

two design options. Chiller operation in

demand-limiting systems may also be

controlled to minimize site peak demand,

resulting in variable chiller output during the peak demand period.

Storage priority and chiller priority are

two alternative operating strategies for

Figure 13 cool storage systems with partial storage . Typical eutectic salt

configuration.(e)

further cool the water, unless humidity

control is not a concern in the application.

Variations: Design and Operating

Strategies

Full storage systems, also known as

load shifting systems, are illustrated

in Figure 14. Full storage systems are

designed to meet all on-peak cooling

loads from storage. On the peak demand

day, the chiller in a full storage system

operates at its capacity during off-peak

hours to charge storage and meet cooling loads occurring during off-peak

hours. This type of system results in

Figure 14. Cool storage design options.(e)

Figure 12. Eutectic salt containers.(e)

(e) Copyright 1994, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. www.ashrae.org. Reprinted by permission from Design Guide for Cool Thermal Storage.
12

FEDERAL ENERGY MANAGEMENT PROGRAM

designs. As the names imply, cooling is

preferentially provided from storage

with storage priority operation and

directly from the chiller with chiller priority operation. The preference is mostly

driven by the relative cost of providing

cooling via either mode. The cost comparison must consider average chiller

efficiency and electricity costs per kWh

for both modes plus storage efficiency

if cooling from storage. Storage priority

generally requires a more complex control scheme to ensure that adequate

cooling capacity will be available late in

the day as storage is being preferentially

depleted. Predictions of remaining cooling load must be combined with measurement of remaining cooling capacity

and knowledge of chiller capacity to

determine the appropriate mix of storage and chiller cooling. Additional discussion of storage priority operating

strategies can be found in ASHRAE

(1993). Chiller priority control is much

simpler. When the cooling load exceeds

the capacity of the chiller, storage is discharged to meet the residual demand.

No predictions of remaining cooling

load for the day are necessary.

Installation

Installation requirements vary significantly among the alternative cool storage systems and depending on whether

a new construction or retrofit scenario

is being considered. Chilled water or

eutectic salt storage systems are the easiest to retrofit because a standard water

chiller can be used and secondary coolant loops coupled with additional heat

exchangers are not usually employed.

Modification or replacement of current

chillers is generally required for any of

the ice storage systems. This is particularly true for ice harvesting and ice slurry

systems because they require specialized evaporators. Ice-on-coil systems

charged via evaporating refrigerant or

secondary coolant below 18°F will also

require new equipment; standard water

chillers are usually adequate for chilling a secondary coolant as low as 18°F,

albeit at reduced capacity and efficiency

compared to chilling water to about

40°F (ASHRAE 1993). Thus, minimal

chiller modifications are required for

cool storage systems designed to be

charged by 18+°F coolant, which

includes many ice-on-coil systems

plus encapsulated ice systems. Many

vendors offer integrated chiller and

storage systems that are particularly

attractive when replacing conventional

cooling systems that are worn out.

Federal Sector Potential

Cool storage technologies have been

successfully applied in thousands of

non-Federal facilities, but only a few

dozen Federal facilities. The potential

for successful Federal application would

appear to be much greater, however,

because Federal facilities tend to have

several characteristics that should make

cool storage generally more attractive

than in other sectors. These characteristics include:

• Relatively large cooling systems that

can take advantage of storage system

economies-of-scale.

• A preponderance of chilled water

cooling systems that are generally

easier to integrate with cool storage

than cooling systems served by

direct-expansion equipment.

• Rate structures characterized by

high-demand charges and/or large

variation in hourly energy charges.

• Older equipment that needs

replacement.

Estimated Savings and Market

Potential

Despite the qualitative advantages

noted above, it is difficult to quantify

the Federal potential (or the non-Federal

potential, for that matter) of cool storage

systems because of the significant impact

that site-specific factors (such as electricity demand profile, electric rate structure,

cooling demand profile, existing cooling

system equipment, etc.) have on the costeffectiveness. A truly accurate assessment

needs to consider each site on an

individual basis. Nevertheless, the

market potential for cool storage has

been estimated for the U.S. Army by

the Construction Engineering Research

Laboratory (Sohn and Cler 1990).

The work by Sohn and Cler focused

on the potential savings in electricity

demand and energy charges from shifting chiller use to off-peak hours. The

overall efficiency of the cooling system

was presumed to be unaffected by the

cool storage system, i.e. there was no

net increase or decrease in energy consumption. Incremental capital costs

were estimated for two scenarios: new

construction or equipment replacement

and retrofit. The first scenario allows

credit for chiller downsizing, but not

the second. Simple rules of thumb were

used to establish the size of the cool storage system required to reduce peak

electricity demand by either 5% or 10%.

Incremental system costs were assumed

to be $80/ton-hour for the new construction or equipment replacement scenario

and $150/ton-hour for the retrofit scenario. Thus, the only site-specific inputs

to the estimate were the electric rates.

The results of the study indicated that

cost-effective application (payback

period of 10 years or less for government investment) of cool storage systems designed to reduce peak electrical

demand by 10% would result in annual

savings of about $12 million for the new

construction/equipment replacement

scenario. This figure was reduced to

about $4 million per year for the retrofit

scenario. The Army represents about

25% of the total Federal floor space, so

a rough estimate of the total Federal

potential for cool storage systems would

be annual savings of about $50 million.

Laboratory Perspective

Thermal energy storage for space cooling

is a relatively mature technology experiencing evolutionary improvements to

older concepts, innovation with newer

concepts, and extension of applicability
13

FEDERAL ENERGY MANAGEMENT PROGRAM

from chilled water systems to packaged

rooftop systems. The impetus for considering cool storage systems (from the

end-user’s perspective rather than the

electric utility’s perspective) was originally driven by high-demand charges

and/or on-peak energy charges and

the opportunity to save on energy costs.

While electric rates are still a significant

motivation for implementing cool storage, many systems are being installed

today on the basis of lower first cost and/

or lower energy consumption as well.

Cool storage systems have become relatively common in the commercial sector,

particularly in applications such as

schools that have high ratios of peak to

average cooling loads. Federal applications have lagged, however, representing only about 1% of the total

population of installed systems. With

many Federal facilities having similar

characteristics to commercial facilities

where cool storage has been successfully installed, broader consideration of

cool storage at Federal facilities seems

warranted. The rough estimate of Federal sector potential described above

also suggests that significantly greater

utilization would be beneficial. Still,

there are no simple rules-of-thumb that

will always identify where cool storage

can be cost-effectively applied. The use

of cool storage or not and selection of the

best cool storage system must be carefully considered via screening studies

on a site-specific basis.

Application

This section addresses the technical

aspects of applying cool storage

technology. The conditions in which

cool storage can be best applied are

addressed. The advantages, limitations, and benefits of each application

are enumerated. Design and integration

considerations for the technology are

discussed, including equipment and

installations costs, installation requirements, maintenance impacts, and utility

incentives and support.

Application Screening

Historically, cool storage has been more

commonly applied in buildings with

relatively high cooling loads, usually

served by central chillers coupled with

chilled water distribution systems. The

majority of applications served peak

cooling demands of 100 tons or more and

required storage capacities of 500 tonhours or more (Potter 1994; E-Source

1998). Several manufacturers now offer

packaged ice storage systems as small

as 100 ton-hours at unit costs that are

essentially the same as larger sizes. These

smaller storage systems are also being

coupled with chillers to retrofit directexpansion (DX) rooftop cooling systems. One manufacturer has developed

a 42 ton-hour storage unit specifically

designed for integration with DX cooling systems. Thus, cool storage equipment is available for practically all types

of buildings. Cost-effectiveness must

be considered on a case-by-case, sitespecific basis, however.

Where to Apply

Cool storage will reduce the average cost

of energy consumed and may potentially

reduce the energy consumption and

initial capital cost of a cooling system

compared to a conventional cooling

system without cool storage. While most

building space cooling applications are

potentially attractive candidates, the

prospects will be especially attractive

if one or more of the following conditions exists.

• Electricity energy charges vary significantly during the course of a day.

• Electricity demand charges are high

or ratcheted.

• The average cooling load is significantly less than the peak cooling load.

• The electric utility offers other incentives (besides the rate structure) for

installing cool storage.

• An existing cooling system is

expanded.

• There is new construction.

• Older cooling equipment needs

replacing.

• Cold air distribution benefits can

be captured.

What to Avoid

In general, applications lacking the

conditions identified above should be

avoided. In addition, the following conditions should also be avoided.

• Lack of operation and maintenance

experience or training with system

equipment, especially where built-up

refrigeration systems are used rather

than packaged chillers.

• Lack of operator training on operating and control strategies for minimizing cooling system life-cycle costs.

• Sites where the space available for

cool storage equipment is limited

or has other, more valuable uses.

• Limited resources for engineering

feasibility studies and system design.

Cool storage systems are inherently

more complicated than non-storage

systems and extra time will be

required to determine the optimum

system for a given application.

Equipment Integration

The specific integration requirements

vary for the different types of cool storage systems. In some cases, multiple

integration options exist for a single

type of cool storage system. Fundamentally, the storage device separates the

generation of chilled coolant from its

delivery to air handling units. Thus, an

extra piping loop (one for charging and

one for discharging storage) with pumps,

valves, and controls is required compared to a conventional system. Typical

system configurations were shown in
14

FEDERAL ENERGY MANAGEMENT PROGRAM

ice slurry systems requires different skills

than for standard packaged chillers.

Equipment Warranties

A one-year warranty is commonly

offered by cool storage system manufacturers on all equipment, parts, and

materials. Labor is not usually covered.

Specific system components (e.g., the

coil in ice-on-coil systems) are warranted for a longer period by some

manufacturers. Other manufacturers

will guarantee performance in terms of

available storage and discharge capacities or the maximum rate of heat gain

through the walls of the tank.

Costs

Costs will vary significantly for cool

storage systems because of the many

different technology options and significant size economies-of-scale for some

components, in addition to variation in

site-specific conditions and individual

vendor offerings. In general, all systems

have a chill-generating device and a chill

storage device, even if the two devices

are closely integrated (e.g., external-melt,

ice-on-coil systems). The following cost

equations can be used to prepare rough

estimates of system costs, suitable for

initial screening of alternatives. A more

rigorous approach based on site-specific

system integration requirements and

vendor quotes for major components

should be used when refining the initial

screening evaluation (see “Refining the

Evaluation” below) and preparing the

final estimate.

Equations 1 and 2 can be used for

estimating the costs of conventional aircooled reciprocating chillers and watercooled centrifugal chillers, respectively

(Means 1999). As indicated, Equation 1

is generally applicable at capacities

Figures 2, 3, 6, 7, 8, 9, 11, and 13. In addition, a common variation to consider is

whether to install the chiller upstream

or downstream of the storage unit as

shown in Figure 15 for an ice-on-coil

system. Installing the chiller in the

upstream position increases chiller efficiency because the coolant temperature

is higher, but reduces the usable storage

capacity because storage is discharged

with a lower temperature coolant. The

opposite effects occur when the chiller

is installed in the downstream position. The two choices present a tradeoff between storage capital costs and

chiller operating costs that should be

considered in a detailed evaluation of

system options.

Maintenance Impact

Chiller and cooling tower maintenance

activities with cool storage are essentially the same as for a conventional

cooling system. However, the chiller

and cooling tower are usually smaller

with cool storage, which should generally reduce the cost of replacement

parts and specifically reduce refrigerant

replacement and cooling tower cleaning and water treatment costs. Chiller

and cooling tower maintenance can

also be conducted while cooling is provided from storage, which benefits

maintenance scheduling.

The addition of a cool storage tank is the

most obvious difference from a conventional cooling system, but incremental

maintenance requirements tend to be

minimal. Water treatment requirements

are the same as for non-storage systems,

but the volume of water to be treated,

hence cost, is greater. Water levels should

be checked at least once a year, or more

often for open tanks. Special attention

needs to be given to the water chemistry

in ice harvesting systems where warm

return water is highly aerated as it’s

sprayed on the ice/water mixture within

the tank. Detailed discussion of water

treatment requirements can be found in

Ahlgren (1987).

Systems using glycol must use a version

intended for HVAC applications that

include corrosion inhibitors and other

additives that allow contact with air.

Glycol chemistry should be checked

annually to ensure that proper concentration of the inhibitors and other additives

exist, as well as to ensure maintenance

of the intended water/glycol mixture.

Cool storage systems usually have more

pumps, control valves, and possibly heat

exchangers than conventional cooling

systems, with periodic maintenance

required for each. Tank inventory sensors

will also require periodic calibration.

Finally, maintenance of refrigeration

equipment such as that used in ice harFigure 15. Upstream and downstream vesting, external melt ice-on-coil, and

chiller configurations.(f)

(f) Copyright 1994, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. www.ashrae.org. Reprinted by permission from Design Guide for Cool Thermal Storage.
15

FEDERAL ENERGY MANAGEMENT PROGRAM

less than 200 tons, while Equation 2 is

generally applicable at sizes greater

than 200 tons.1 Both equations are based

on the equipment capacity for producing chilled water at standard ARI rating

conditions. Equations 1 and 2 can be

used directly to estimate the costs of

water chillers used in conventional cooling systems and for systems using chilled

water or eutectic salt storage.

(1)Air-Cooled Reciprocating Chiller

Installed Cost = $11,900 + 591*Twc

Where Twc = nominal water chiller

capacity in tons, from 20-200 tons.

(2)Water-Cooled Centrifugal Chiller

Installed Cost = $57,700 + 307*Twc

Where Twc = nominal water chiller

capacity in tons, from 200-1500 tons.

Equations 1 and 2 can also be used for

estimating the cost of chillers used to

make ice in ice-on-coil storage systems

by applying an adjustment factor.

Operation at ice-making evaporating

temperatures reduces capacity by about

1/3 compared to water chilling; the

actual ratio depends on the evaporating temperature required (varies by as

much as 10°F depending on the type

and specific model of ice-on-coil storage). Alternatively, the equivalent water

chilling capacity is about 50% higher

than the ice generating capacity. Therefore, the cost of chillers for ice-on-coil

storage systems can be estimated using

equations 1 or 2 by first multiplying the

required ice-generating capacity by 1.5.

Water-cooled systems require cooling

towers to cool condenser water. Cooling tower costs can be estimated using

Equation 3 (Means 1999). The same

equation applies whether the cooling

tower is applied to a water-cooling or

ice-generating “chiller.”

(3)Cooling Tower Installed Cost =

$982*Thr

0.64

Where Thr = heat rejection capacity

in tons, from 60-1000 tons2

Dynamic ice-generators are generally

more expensive than the chillers used

with static ice-on-coil systems. Ice slurry

generators are currently offered in

modular units resulting in an installed

cost of about $1000/ton of ice at capacities of 100 tons or more. Ice-harvesting

generators are typically slightly more

expensive as indicated by Equation 4

(ASHRAE 1993).

(4)Ice-Harvesting Generator Installed

Cost = $195,000 + 990*Tig

Where Tig = ice generating capacity

in tons, from 200-1000 tons

Chilled-water storage costs depend on

the difference between water supply and

return temperature in addition to the size

of the storage unit. For example, the same

equipment would have twice the storage capacity if operated through a 20°F

differential compared to a 10°F differential. Alternatively, the same capacity

could be achieved with a tank that is

50% smaller. Equations 5 through 7 can

be used for estimating chilled water storage costs for three alternative supply

and return water temperature design

assumptions (EPRI 1992). Similarly,

Equation 8 can be used for estimating

storage-related costs for dynamic ice systems using ice-harvesting or ice slurry

generators. Again, the vessel is essentially the same as for chilled water storage, but costs per ton-hour are lower

because of the higher cooling density

of ice compared to water.

(5)10°F (T Chilled Water Storage Installed

Cost = 802*(TH)0.686

Where TH = storage capacity in tonhours, ton-hours from 600-6000

(6)15°F ∆T Chilled Water Storage Installed

Cost = 616*(TH)0.686

Where TH = storage capacity in tonhours, ton-hours from 900-9000

(7)20°F ∆T Chilled Water Storage Installed

Cost = 498*(TH)0.686

Where TH = storage capacity in tonhours, ton-hours from 1200-12,000

(8)Dynamic Ice Storage Installed Cost =

211*(TH)0.686

Where TH = storage capacity in tonhours, ton-hours from 4,000-40,000

Ice-on-coil and encapsulated ice storage

system costs are dominated by the heat

transfer surface, which is the piping or

coils for the former and the flexible

encapsulating material for the latter.

Storage capacity, hence cost, is directly

proportional to the heat transfer area

and the amount of ice that can be generated and stored at full charge per unit of

heat transfer area. The installed cost for

ice-on-coil and encapsulated ice storage

is about $70/ton-hour.3

 Although there

could be economies-of-scale associated

with the tank or containment vessel,

most ice-on-coil systems come in preassembled tank and coil packages of

moderate individual capacity with larger

capacity needs met via multiple tanks.

Thus, the cost per ton-hour for these

types of systems is usually independent

of the number of ton-hours required.

Similar to ice-on-coil and encapsulated

ice systems, eutectic salt system costs are

dominated by components (the salt and

its enclosure) that vary directly in size

and cost with the required system capacity. Again, the tank or vessel represents

a relatively small portion of the total storage system cost, so its economies-of-scale

are overshadowed by the cost of the salt

and its enclosure. The installed cost of

1

 In this section and throughout this FTA, a “ton” means 12,000 Btu per hour. This rating is derived from the average hourly cooling rate

achieved from melting one ton (2000 pounds) of ice over a 24 hour period (2000 pounds * 144 Btu/pound / 24 hours = 12,000 Btu/hour). Thus,

a 100-ton ice generator has a cooling capacity of 1.2 million Btu per hour and would be able to produce roughly 100 tons (200,000 pounds) of

ice in 24 hours.

2

 Note that cooling tower capacity is greater than chiller capacity because the energy input to the chiller must be rejected along with the cooling

load being served by the chiller.

3

 Based on information collected from Baltimore Air Coil, Calmac, Chester-Jensen, Cryogel, Dunham-Bush, Fafco, and Girton Manufacturing.
16

FEDERAL ENERGY MANAGEMENT PROGRAM

eutectic salt storage is about $125/tonhour (ASHRAE 1993).

In addition to the chiller and storage

components, installation of a cool storage system will require miscellaneous

pipes, valves, pumps, instrumentation,

controls, and possibly heat exchangers.

The requirements for this miscellaneous

hardware, hence costs, vary significantly

depending on site-specific conditions.

The costs for these components can be

ignored when conducting initial screening studies, but should be estimated

from an assessment of specific requirements when preparing the final design

evaluation.

Utility Incentives and Support

Utilities offer various forms of financial

and technical support for cool storage

systems. Examples include rebates specific to cool storage, rebates for peak

load reduction, and cost-sharing of feasibility studies. The following utilities

provided incentives and/or support

specific to cool storage systems as of

spring 1999, according to a survey conducted by Energy User News (Cahners

Business Information 1999a and 1999b).

Other programs, such as those targeting

chillers, HVAC, load management, etc.,

may also apply. Incentive and support

programs are subject to change, particularly as the electric utility industry

deregulates. Therefore, prospective

users of cool storage systems should

contact their electric utility to see what

incentives are available and applicable.

Alabama Power Company: $100/kW

deferred; $5000 for feasibility studies

Baltimore Gas and Electric Company:

$200/kW shifted; $15,000 for feasibility

studies

Columbia Water and Light: Rate inventive; no specific information available

Delmarva Power and Light: $140/kW

shifted with $100,000 maximum

Florida Power and Light: No specific

information available

Gainesville Regional Utilities: Rebate

based on tonnage; no specific information available

GPU Energy: No specific information

available

Houston Power and Lighting: $300/kW

shifted

Lansing Board of Water and Light:

$100/kW of installed equipment

Northern States Power Company: No

specific information available

Pasadena Water and Power Company:

$5000 for feasibility studies

Riverside Utility District: $5000 for feasibility studies; $200/kW shifted off peak

South Carolina Public Service Authority:

$200/kW shifted off-peak; co-funding of

feasibility study

United Illuminating Company: $400/kW

shifted or $400/ton shifted; feasibility

study grants

Technology Performance

Several thousand cool storage systems

have been installed in the United States,

but only about 1% of these have been at

Federal facilities. The majority of systems have used ice-on-coil technology,

but stratified chilled water systems have

also been moderately popular. Both iceon-coil and stratified chilled water are

mature technologies, but evolutionary

improvements are continuously implemented by manufacturers. The experiences with cool storage at three Federal

facilities are summarized below; see section on “Who is Using the Technology”

for contact information.

An ice-on-coil system installed at the

Ralph H. Johnson VA Medical Center in

Charleston, South Carolina, was originally designed to provide the entire

on-peak cooling load from storage, but

subsequent building expansions now

require partial chiller operation on

peak cooling days. The facility was

driven to consider cool storage as a

means of reducing its energy costs.

A $1 million rebate offered by the serving electric utility provided a huge

incentive and served to ensure project

cost-effectiveness. Initial problems were

experienced with the chiller, but not the

storage system itself. Chiller problems

were probably caused by disassembly

of the chiller during installation, which

was required to fit the chiller into the

mechanical room. These problems have

since been ironed out. Other minor performance problems developed initially

because no operating guidelines were

in place. Standard operating procedures

have now been established for each

month and performance has been consistently good. Electricity cost savings

are typically around $5000 per month

during the cooling season at this 500,000

square foot facility.

A 10,000 ton-hour stratified chilled water

tank was tied into an existing district

cooling system serving 10 buildings at

the Sandia National Laboratories in

Albuquerque, New Mexico. Installation

of the storage system allowed extension

of the district cooling system to a new

150,000 square foot building without

adding additional chiller capacity. In

addition, annual energy savings are

expected to be $200,000 per year. The

system was installed and has operated

without any unexpected problems. The

system was designed to allow several

different operating strategies, but did

not require the installation of any new

pumps. The biggest problem experienced

was overcoming internal resistance to

changes of any kind. Therefore, site

personnel advise working hard to get

“buy-in” from management and maintenance personnel. Also suggested is

thorough consideration of alternative

design options before committing to a

single approach.

A full-storage, ice-on-coil system was

installed at the U.S. Army Reserve

Center in Monclova, Ohio, when this

54,000-square-foot facility was built

in 1996. The facility received a 1998

Engineered Systems Engineering Team

Award for the cool storage system and
17

FEDERAL ENERGY MANAGEMENT PROGRAM

other energy management features. Estimated energy savings for the cool storage system are about $1000 per month

during the cooling season. In general,

the system works well, but they have

experienced a few minor problems.

Occasionally, the building is occupied

at night, which increases the cooling

load and doesn’t allow the storage system to be fully charged. Basically, the

system wasn’t designed to handle this

type of occupancy pattern. As a result,

the chillers had to be operated during

the day and it takes a few days to fully

recharge and return to normal operation. As site personnel point out, “If

your cooling load is nearly constant,

24 hours a day, it won’t work.”

Evaluating Cool Storage

Systems

The process of identifying and evaluating alternatives is more complicated

for cooling systems using cool storage

than for those without. The increased

complexity is driven by the plethora

of alternative storage types and system

configurations plus the need to consider

cooling loads and cooling system operation for a complete charge and discharge

cycle rather than just a single design

point. The evaluation process consists

of the following steps:

• determine cooling requirements

• identify alternative storage types and

system configurations to be evaluated

• conduct screening evaluation of

alternatives

• refine screening evaluation results for

preferred alternative(s).

Each of these steps is briefly discussed

on the following pages.

For a more detailed discussion the reader

is referred to the list of design and installation guides provided on page 26.

Cooling Requirements

Cool storage system evaluation and

design requires knowledge of hourly

cooling loads for the peak design day

(for daily storage cycles or for the peak

design week for weekly storage cycles)

in addition to the peak design hour.

Note that the peak design hour may

not necessarily occur during the peak

design day, but the cool storage system

must be sized to meet both requirements. In addition to requiring more

cooling load data than for a non-storage

design, there is a greater need for that

data to be accurate. For example, if the

chiller in a non-storage system is undersized, the building it is serving is likely

to be too warm for a few hours a day for

a few days a year. However, as ambient

conditions cool during the evening and

early morning hours, the non-storage

system will be able to catch up. Most

cool storage systems have smaller

chillers, however, and rely on storage

to provide part or all of the cooling load

during the peak afternoon hours. If a

storage system is undersized, it will not

be able to catch up at night and have

storage adequately charged for the

following day. If the storage system is

undersized and there are several consecutive days of weather near peak

design conditions, overheating problems will likely accumulate. In short,

the smaller chiller sizes associated with

storage systems provide less reserve

capacity compared to non-storage systems, which puts a premium on correctly

specifying the design conditions. Practical approaches for dealing with this

concern include selecting more conservative design weather conditions (e.g.,

design for “99%” conditions rather than

“97.5%” conditions) or applying a more

conservative safety factor when sizing

the chiller and storage components of a

cool storage system. However, spending

additional effort to accurately define the

design cooling conditions is the best

form of design insurance.

Cooling load profiles developed for

generic buildings similar to the application being considered are adequate for

the initial screening evaluation, but

more accurate load estimation procedures are required for the revised evaluation and preparation of system design

specifications. Cooling load calculations

are discussed in detail in ASHRAE’s

Handbook on Fundamentals (ASHRAE

1997). Note that the cooling load must

account for heat gains from fans, ducting, piping, and pumps, as well as the

load delivered to the conditioned

space. In addition, heat gain through

the wall of the storage vessel and availability losses within the vessel must be

accounted for when sizing storage and

the chiller4

. In retrofit situations, measurement of cooling loads at design

conditions is preferred. If measurements

at design conditions are not available,

measurements at other conditions could

be used to calibrate building load simulation models and the simulation models used to predict cooling loads at

design conditions.

Identifying Alternatives

With a plethora of storage unit and

system configuration possibilities, the

number of alternatives to be evaluated

quantitatively should be minimized by

judicious, qualitative, pre-screening.

With this objective in mind, the following rules-of-thumb are offered for prescreening purposes.

Chilled water storage is more compatible with standard chilled water cooling

systems than the various ice storage

systems. In general, this makes chilled

water storage relatively attractive for

retrofits, and particularly in cooling

capacity expansion situations. Chilled

water systems will look their best where

4

 Mixing and/or conduction across the thermocline within a chilled water storage tank significantly increases the chilled water discharge temperature near the end of each storage cycle. Similarly, the coolant discharge temperature rises at an increasing rate in ice storage systems near

the end of each discharge cycle due to ineffective heat transfer between the discharge coolant and the dwindling amount of stored ice.
18

FEDERAL ENERGY MANAGEMENT PROGRAM

relatively large storage requirements

can take advantage of tank economiesof-scale and where the availability of

space is not a significant concern.

The applicability of eutectic salt storage

is similar to chilled water. However, its

higher energy density makes it more attractive than water where limited space

is a greater concern than storage cost or

a slightly higher discharge temperature.

Ice storage systems are required to take

advantage of cold air distribution benefits and where limited space is available. Ice storage systems minimize tank

size and cost, so are generally more economical at smaller capacities where tank

costs are a substantial portion of the total

system cost.

Ice-harvesting and ice slurry systems

separate ice generation from ice storage,

resulting in lower storage-related costs

than other systems. However, the icegenerators for both of these types of

systems are more expensive than other

systems. Thus, ice harvesting and ice

slurry systems look their best in applications with a large ratio of storage capacity to storage charging capacity. This

would suggest considering a weekly

storage cycle as well as a daily storage

cycle for these two options. Ice harvesting

and ice slurry systems are also capable

of providing high discharge rates.

Most ice-on-coil and encapsulated ice

storage systems use standard packaged

chillers and secondary coolants for charging, which minimizes ice-generating

costs and ice storage system costs for

most applications. Internal-melt, iceon-coil storage and encapsulated ice

storage allow partial storage without

incurring an efficiency penalty during

the subsequent ice-building period as

happens with external-melt, ice-on-coil

systems that are partially discharged.

External-melt systems, like ice harvesting and ice slurry systems, offer the

highest discharge rates. External-melt

systems may also be directly charged

with refrigerant, which offers efficiency

advantages, but refrigeration equipment

complexities compared to packaged

chillers with secondary coolants.

The three basic configuration options

are full storage and partial storage in

load-leveling or demand-limiting versions. Full storage results in the greatest

savings in on-peak electricity charges,

but requires larger, more expensive,

chillers and storage units. Thus, full

storage should be considered where

there are high demand charges, annually ratcheted demand charges, and/or

a large differential between peak and

off-peak electricity energy charges.

Short discharge periods are also particularly beneficial to the economics of

full storage system designs.

Equipment sizes and capital are minimized with partial storage, load-leveling

designs, but on-peak electricity charges

are reduced the least of the three basic

configurations. Thus, situations with a

high ratio of peak to average cooling

loads are attractive for partial storage

configurations as are situations with

minimal incentive from the electric

rate structure. Partial storage, demandlimiting designs are a hybrid of the two

other configurations and are probably

best considered as a possible variant of

one of the other two principal options.

Screening Alternatives

The initial screening of alternatives follows the steps bulleted below, starting

with the design load profile and applicable utility rate schedule. Note that differences in annual energy consumption

generally have a smaller economic

impact than differences in equipment

costs and electricity demand when comparing alternatives, so is usually ignored

in the screening process.

The initial screening steps are:

• size chiller and storage

• estimate chiller and storage capital

cost

• estimate annual demand savings

• calculate system life-cycle cost

• select preferred system(s) for detailed

analysis.

For non-storage systems, the chiller is

sized to meet the peak hourly load. With

storage, the chiller is sized to meet the

cooling load over the storage cycle, typically a 24-hour period. Thus, for partialstorage systems, the chiller will always

be smaller than for a non-storage system, while for full-storage systems, the

chiller may be smaller or larger than for

a non-storage system, depending on the

design load profile and the length of the

on-peak period.

At the simplest level, chiller capacity

equals the design-day cooling load

divided by the number of chiller operating hours. For a partial-storage system,

the number of chiller operating hours is

24, i.e., the chiller operates at full capacity for 24 hours on the design day. For

a full-storage system, the number of

chiller operating hours is 24 minus the

length of the peak-demand period.

For greater accuracy the calculation of

nominal chiller capacity should consider the relative chiller capacity when

charging storage, direct cooling during

the on-peak period, and direct cooling

during the off-peak period. Capacity

may be different than the nominal rating

due to differences in evaporating or condensing conditions and/or because of

different assumptions regarding selection of full storage or partial storage

(with load-leveling or demand-limiting

options) designs. Thus, the nominal

chiller capacity equals the design-day

cooling load divided by the sum of the

number of chiller operating hours in

each mode, with the number of hours

in each mode multiplied by the average capacity in that mode relative to

the nominal capacity (see Equations 9

and 10).

(9)Nominal Chiller Capacity = Total Cooling Load/Adjusted Chiller Operating

Hours

(10)Adjusted Chiller Operating Hours =

H1

CR1 + H2CR2 + H3CR3
19

FEDERAL ENERGY MANAGEMENT PROGRAM

Where H1 = hours charging storage

CR1

 = capacity relative to nominal

conditions while charging

H2

 = hours direct cooling during

on-peak period

CR2

 = capacity relative to nominal

conditions while cooling during

on-peak period

H3 = hours direct cooling during

off-peak period

CR3

 = capacity relative to nominal

conditions while cooling during

off-peak period

Note that if the nominal chiller capacity

calculated via Equations 9 and 10 is

greater than the load for any hour during the direct cooling mode, then the

chiller capacity must be recalculated via

an iterative procedure illustrated in the

Design Guide for Cool Thermal Storage

(ASHRAE 1993).

The required storage capacity is equal

to the total cooling load minus any

load provided directly by the chiller

or from storage while storage is being

charged. Similar to the calculation of

nominal chiller capacity, cooling provided directly by the chiller or from

storage while storage is being charged

must consider the variation in chiller

capacity while operating in these different modes, as shown in Equations 11

and 12.

(11)Nominal Storage Capacity = Total Cooling Load - Directly Served Load

(12)Directly Served Load = NCC*(H2

CR2 +

H3

CR3) + CAPCH

Where CAPCH = capacity provided from

storage while simultaneously charging

storage and NCC = the nominal chiller

capacity.

Note that in some cases the actual load

met from direct cooling will be less

than NCC*H2CR2 or NCC*H3CR3 if the

demand for direct cooling is less than the

chiller’s capacity. In this case, the actual

capacity provided must be used. In short,

care must be taken to keep track of the

cooling loads and expected provision of

cooling from the chiller and/or storage

on an hourly basis. Also note that equations 11 and 12 calculate the nominal

storage capacity, suitable for a screening analysis. The actual required storage

capacity must be determined via an

hour-by-hour simulation of performance

that captures the interactions of the chiller,

storage, and the load. In particular, all

storage systems suffer from an increasing rise in discharge temperature near

the end of a discharge cycle that effectively reduces the useful capacity from

its theoretical maximum.

Sample Calculations

Chiller and storage sizing for a screening evaluation is illustrated through

the following example. The example is

based on a partial storage, load-leveling

system design with ice storage. Compared to its rated capacity at standard

ARI conditions, the relative chiller capacity is presumed to be 0.8 in the storage

charging mode and 0.9 in the direct cooling mode. Design cooling day cooling

loads, chiller operation, and storage

operation are presented in Table 1 and

Figure 16. The cooling load builds in the

late morning, peaks in mid-afternoon

and decays to its minimum daily value

in the early morning. The utility on-peak

period is shown as running from noon

until 6:00 p.m., but this has no impact on

a partial storage, load-leveling design.

The total daily load is 48,500 ton-hours.

Thus, if the chillers were able to provide

their nominal capacity while charging

storage and direct cooling, the required

capacity would be 2021 tons (48,500 tonhours/24 hours = 2021 tons). This is the

average actual capacity the chillers will

need to provide to meet the daily cooling demand. The required nominal capacity will be higher because the chiller

operates at less than nominal capacity.

In order to achieve an average net capacity of 2021 tons the average net capacity

while charging (where the relative capacity is 0.8) will be less than 2021 while

the average net capacity while direct

cooling (where the relative capacity is

0.9) will be more than 2021. These approximations of net capacity allow for

reasonable assumptions regarding the

chiller and storage operating modes

during each hour of the day that will be

verified or refuted after determining the

nominal chiller capacity. For example,

with a direct cooling capacity of at least

2021 tons, the chillers are assumed to be

charging storage during hours 1-9 and

21-24 and directly cooling for hours

10-20. The cooling load is met by discharging storage alone during hours 1-9

and 21-24, while storage discharge and

direct cooling are required to meet the

load for hours 10-20.

The nominal chiller capacity is calculated by plugging the assumptions presented above into Equations 9 and 10.

Nominal Chiller Capacity = 48,500/

((13*0.8)+(6*0.9)+(5*0.9) = 2389.2 tons5

The actual chiller capacity is 1911.3 tons

(2389.2 * 0.8) in the storage charging

mode and 2150.2 tons (2389.2 * 0.9) in

the direct cooling mode. 2150.2 is less

than the cooling load for all hours presumed to be in the direct cooling mode

and 1911.3 is greater than the cooling

load for all hours where storage is being

charged and discharged. Thus, no further adjustments of the initial assumptions are necessary.

The nominal storage capacity is calculated by plugging the assumptions presented above into Equations 11 and 12.

Nominal Storage Capacity = 48,500 -

{2389.2*[(6*0.9)+(5*0.9)]+17,200} = 7,647

ton-hours

The chiller and storage capacity calculations are confirmed by the figures

shown in Table 1, which illustrate the

charging and discharging of storage

from no stored energy in hour 20 to a

maximum of 7,647 ton-hours in hour 9.

5 The capacity and cost figures used in this section have not been rounded off so that the reader can more easily duplicate the calculations.
20

FEDERAL ENERGY MANAGEMENT PROGRAM

The nominal chiller capacity (2389 tons)

required for the storage system would

probably be served by two 1195-ton

units, with each unit costing $424,565

based on Equation 2. Assuming ice-oncoil storage (at $70/ton-hour; see prior

section on costs), the cost of the storage

unit would be $535,290. Thus, the total

storage system cost would be $1,384,420.

A water chiller for a conventional system

would need to have an actual capacity

of 3500 tons or a nominal capacity of

3888.9 tons (3500/0.9) to provide 3500

tons during the on-peak period. A total

capacity of 3888.9 tons would probably

Table 1. Chiller and Storage Sizing Example

Load From Load From Charge to Storage

Utility Load, Chiller Storage Chiller, Storage, Storage, Balance,

Hour Period Ton-Hours Mode Mode Ton-Hours Ton-Hours Ton-Hours Ton-Hours

1 off-peak 1200 CH CH/DCH 0 1200 1911 1,957

2 off-peak 1100 CH CH/DCH 0 1100 1911 2,768

3 off-peak 1000 CH CH/DCH 0 1000 1911 3,679

4 off-peak 900 CH CH/DCH 0 900 1911 4,691

5 off-peak 800 CH CH/D CH 0 800 1911 5,802

6 off-peak 1000 CH CH/DCH 0 1000 1911 6,713

7 off-peak 1300 CH CH/DCH 0 1300 1911 7,325

8 off-peak 1600 CH CH/DCH 0 1600 1911 7,636

9 off-peak 1900 CH CH/DCH 0 1900 1911 7,647

10 off-peak 2200 DC DCH 2150 50 0 7,598

11 off-peak 2500 DC DCH 2150 350 0 7,248

12 off-peak 2800 DC DCH 2150 650 0 6,598

13 on-peak 3100 DC DCH 2150 950 0 5,648

14 on-peak 3300 DC DCH 2150 1150 0 4,499

15 on-peak 3500 DC DCH 2150 1350 0 3,149

16 on-peak 3300 DC DCH 2150 1150 0 1,999

17 on-peak 3100 DC DCH 2150 950 0 1,049

18 on-peak 2800 DC DCH 2150 650 0 400

19 off-peak 2500 DC DCH 2150 350 0 50

20 off-peak 2200 DC DCH 2150 50 0 0

21 off-peak 1900 CH CH/DCH 0 1900 1911 11

22 off-peak 1700 CH CH/DCH 0 1700 1911 223

23 off-peak 1500 CH CH/DCH 0 1500 1911 634

24 off-peak 1300 CH CH/DCH 0 1300 1911 1,245

Totals 48,500 23,653 24,847

CH = Charging

DCH = Discharging

DC = Direct Cooling

Figure 16. Chiller and storage sizing example.

0

1000

2000

3000

4000

5000

6000

7000

8000

0 6 12 18 24

Hour of the Day

Cooling Load

Chiller Output

Storage Balance

Ton-Hours of Cooling

on-peak
21

FEDERAL ENERGY MANAGEMENT PROGRAM

require three 1296.3-ton units, with each

unit costing $455,663 according to Equation 2 for a total conventional chiller cost

of $1,366,989. Thus, the initial capital

cost of the storage system would be

$17,431 more expensive than the conventional system. Differences in cooling

tower costs should also be considered

when refining the initial screening results.

The screening evaluation must also estimate the reduction in electricity costs

associated with the cool storage system.

Electricity costs can be reduced from a

reduction in demand charges and/or

energy charges. The importance of

evaluating one or the other or both depends on the site-specific electric rate

structure.

The evaluation of demand charge savings starts by estimating the reduction

in on-peak demand when comparing

conventional and storage cooling systems. In the example, the peak cooling

demand of 3500 tons would create a

peak cooling system electric demand

of 3076 kW for a water chilling system

[including the electrical demand of the

chiller compressor, cooling water pumps

and cooling tower fan (if water-cooled)

or condenser fan (if air-cooled)] with a

COP of 4.0. The cool storage system

chillers need only provide 2150 tons of

cooling during the on-peak period, so

the electrical demand of its water chilling

system components would be 1890 kW

at a COP of 4.0 or a reduction of 1186 kW.6

Note that the peak electrical demand for

the chilled water pumps will be approximately the same for the two systems

and any difference can be ignored for

the screening study. Differences in

supply and return water temperatures, flow rates, and pumping energy

should be considered when refining

the analysis for alternatives passing the

initial screening.

For a typical monthly demand charge

of $10/kW, the 1186 kW demand reduction translates into savings of $11,860 for

the peak month. Calculation of demand

savings in other months requires additional assumptions or knowledge of

the variation in peak cooling loads from

month to month, the type of demand

charge, and whether the partial storage

system is operated in chiller priority or

storage priority mode. By definition, the

peak cooling loads will be less during

the other 11 months of the year. In addition, the on-peak period often changes

and demand charges are often lower in

the winter than in the summer. In short,

the annual demand charge savings will

usually be considerably less than 12 times

the peak monthly savings. Lacking

any better information, assuming that

annual demand savings are equivalent to 8 months like the peak demand

month for partial storage systems and

6.5 months for full storage systems is

reasonable (ASHRAE 1993). Thus,

annual demand charge savings would

be estimated at $94,880 ($11, 860 * 8) for

the example cooling system.

Clearly, these rules-of-thumb for estimating the annual demand charge savings should only be applied for initial

screening purposes and not for the more

refined analyses that follow. Even for the

initial screening, additional analysis of

cooling loads is required where the differential between on-peak and off-peak

energy charges is thought to be significant. At a minimum, the annual cooling

load must be segregated into that occurring during peak and off-peak periods

for each alternative cooling system. System COPs should be estimated for both

periods to determine kWh consumption

and the applicable energy charge applied

to estimate energy costs and the savings

relative to the reference non-storage system. For selecting the best system configuration and operating strategy from

similar options or finalizing component

sizing and system design specifications,

an evaluation based on hourly cooling

loads for the full length of the cooling

season is a requisite.

The results of the screening evaluation

should determine which, if any, of the

cool storage system alternatives is worthy of further investigation. Unless the

least costly system also incurs the lowest electricity costs, the life-cycle cost of

each alternative should be calculated to

develop a ranking. Although the absolute accuracy of the screening results is

relatively poor, the relative accuracy

for comparative purposes is generally

adequate thanks to the use of common

ground rules and assumptions. Still,

judgment must be applied regarding

what constitutes a significant difference

and how many alternatives should be

carried forward.

Refining the Evaluation

A more detailed evaluation is required

to select the best system from those

retained from the screening evaluation

and to prepare the final system design.

The most important refinement may be

to develop better estimates of cooling

loads and ambient air conditions while

operating the prospective cooling systems. The quality of the evaluation and

resulting design can be no better than

the quality of the underlying cooling

load and weather data.

Typical building load profiles, while

adequate for the screening evaluation,

are not adequate for selecting the best

system and preparing its design. Hourly

cooling load data allow much greater

accuracy, but may be difficult to obtain.

Metered chilled water production or

chiller power input may be available

in some cases. Alternatively, building

energy simulation models could be

used to estimate hourly cooling loads.

6

 The peak electric demand for the cooling system usually coincides with the peak electric demand for the entire facility, but this is not necessarily true. More generally, the peak electric demand for the alternative cooling systems should be compared for the hour creating the peak

billing demand.
22

FEDERAL ENERGY MANAGEMENT PROGRAM

Another option would be to repeat

calculations used to determine hourly

loads for the peak annual demand day

for the peak demand days in each of the

other 11 months. This will allow a more

accurate assessment of demand charge

reduction (remember that its not necessarily the peak cooling system demand

that’s important, but the cooling system

demand coincident with peak demand

at the utility metering point). Barring

the availability of metered or simulated

hourly load data, reasonable assumptions

will need to be made to estimate monthly

cooling loads and the portions occurring

during on-peak and off-peak periods.

Accurate knowledge of hourly loads is

required where the difference between

on-peak and off-peak electricity energy

charges is important to the economic

justification of the cool storage system.

The refined analysis needs to specifically

consider how the cool storage system

will be integrated and operated with

the rest of the cooling system and the

impact of integration details on performance. Operation and control schemes

(e.g., chiller priority or storage priority)

must be selected. Flow diagrams identifying the requisite piping, pumps, valves,

and heat exchangers must developed.

System performance should be simulated for the design day at a minimum

or for entire year if possible. The simulation should evaluate supply and return

fluid temperatures while charging and

discharging, supply air temperature

to the conditioned space, and energy

inputs to the cooling system. Special

attention should be paid to the rise in

storage discharge and supply air temperatures as storage is discharged to

ensure the cooling load can be comfortably met. The actual storage capacity

required will be greater than the theoretical storage capacity by a margin that

varies depending on the storage technology and discharge rate required when

the storage system is nearly discharged.

Vendor quotes should be obtained for

major equipment components if not

already done for the initial screening

evaluation. The costs of all ancillary

equipment (e.g., pumps, piping, valves,

heat exchangers) need to be estimated

and included in the economic evaluation. Maintenance cost differences

should also be evaluated and incorporated into the analysis.

Case Study

An internal-melt ice-on-coil thermal

energy storage system was installed

at a GSA office building in Pittsburgh,

Pennsylvania, as part of a project

upgrading the entire chilled water

cooling system. Originally driven by

the need to replace CFC refrigerants,

the project eventually evolved to include

replacement of the chillers and cooling

tower and installation of the cool storage

system and variable speed drives on

the chilled water and condenser water

pumps. The system was installed during the winter of 1995-1996 and has

been operating successfully since.

Facility Description

The William S. Moorhead Federal

Building is a 23-story, 788,000 square

foot structure constructed in 1963.

Various Federal agencies occupy the

building that is managed by the GSA.

Occupancy is concentrated on weekdays from 8:00 a.m. till 5:00 p.m. with

occasional usage during other hours.

Existing Technology Description

The existing cooling system consisted of

two 990-ton centrifugal chillers with an

efficiency of about 0.90 kW/ton. Both

chillers used CFC-12 refrigerant and

had a history of leaking. Two constantspeed 125 hp chilled water pumps

provided 2866 gpm at 125 feet of head.

The 75 hp condenser pumps provided

2487 gpm at 80 feet of head. Heat rejection was served by a single 1980 ton

roof-mounted cooling tower.

New Technology Equipment

Selection

Initial investigations examined the feasibility of retrofitting the existing chillers

with a non-CFC refrigerant and installing variable speed drives (VSDs). While

it was possible to simply change the

refrigerant and installing the VSDs would

improve efficiency, replacement with

new, high-efficiency non-CFC chillers

was more cost-effective. At this point

in the project development process,

Duquesne Light Company, the serving

utility, encouraged the GSA to consider

a cool storage system. By using cool storage, the cooling capacity of the replacement chillers was reduced by nearly

40%, to two 600-ton units. The new

chillers have a full load efficiency of

0.60 kW/ton at standard rating conditions and 0.75 kW/ton when operating

in the ice-making mode. Constraints on

physical space dictated an ice storage

system rather than chilled water; the ice

storage units were installed in a basement space previously used for storage

and shops. Thirty-nine modular ice

storage units were installed with a total

capacity of 7410 ton-hours.

Savings Potential

Installation of the cool storage system

reduced the size and cost of the new

chillers and also resulted in reduced

demand charges by minimizing chiller

operation during the peak demand

period. During a typical summer weekday, the ice storage system is charged

from 6:00 p.m. until 6:00 a.m. the following morning. Storage is discharged from

noon until 4:00 p.m., the utility’s peak

demand period, to minimize on-peak

chiller operation in this partial storage

type system. The chillers are operated

as needed during the other hours of the

day to directly meet the building cooling

load. On relatively mild summer days

and when cooling during late spring

and early fall months, the chillers don’t

need to be run during the peak demand

period at all. The lower chilled water

delivery temperature possible with an

ice storage system also makes it possible

to consider the benefits of cold-air distribution in an anticipated future replacement of the building’s airside systems.
23

FEDERAL ENERGY MANAGEMENT PROGRAM

Life-Cycle Cost

The project cost $1.6 million, which

included removal and replacement of

existing chillers and cooling towers, the

cool storage system, plus pumps, heat

exchangers, and other miscellaneous

minor equipment. Monthly savings

were estimated to range from $60,000

to $80,000 in the feasibility study, which

was based on a simulation of building

loads and equipment performance.

Actual total energy use has been higher

than expected, but building use and

cooling loads have also increased from

that assumed in the feasibility study, so

the savings estimate may still be valid.

Life-cycle cost savings were calculated

to be $10,447,177 using QuickBLCC. The

results of the QuickBLCC calculation are

presented in detail in Appendix B. BLCC,

the Building Life-Cycle Cost Software

developed by NIST, is described in

Appendix A.

Implementation and PostImplementation Experience

The major components of the new cooling plant (chillers, cooling tower, and

ice storage units) were installed first,

followed by piping, pump, and control

revisions. A new electronic control system replaced the old pneumatic system

to enhance energy savings and improve

zone comfort. After installation, the new

system was subject to a commissioning

procedure by the GSA. According to

Jerry Bower, Maintenance and Operations Foreman, the system has generally

worked well. They have been able to

keep the building just as cool as the old

system, despite having downsized the

chillers by 40%. During peak cooling

periods, the two chillers operate while

the storage system discharges. “The system acts like three 600-ton units,” says

Jerry. They have experienced a few

minor problems. The first control system was not Y2K compliant, so had to

be upgraded. Other component upgrades (e.g., valves, pumps) have also

been implemented over time. “These

things should have been done up front,

but we didn’t have enough money,”

said Jerry. Jerry would also like to have

more storage capacity, but they were

short on space as well as money. In

summary, Jerry notes, “We were all

skeptical at first, but it’s been proven

and is working fine.”

The Technology in Perspective

Cool storage technologies of one type or

another have been successfully applied

in several thousand locations to reduce

energy costs, reduce chiller capacity and

cost, and save energy. Relatively few of

these applications have been in the Federal sector, however. This is unfortunate,

because Federal facilities tend to have

several characteristics that should make

cool storage generally more attractive

than in other sectors. These characteristics include:

• Relatively large cooling systems that

can take advantage of storage system

economies-of-scale.

• A preponderance of chilled water

cooling systems that are generally

easier to integrate with cool storage

than cooling systems served by

direct-expansion equipment.

• Rate structures characterized by high

demand charges and/or large variation in hourly energy charges.

• Older equipment that needs

replacement.

On the other hand, Federal facilities often

suffer from the following conditions that

tend to make cool storage less attractive:

• Lack of operation and maintenance

experience with refrigeration

equipment used in some cool storage systems.

• Lack of training on operating and

control strategies for minimizing

cooling system life-cycle costs.

• Limited resources for engineering

feasibility studies and system design.

Recognition of these constraints suggests that Federal energy managers

may need to lean toward selection of

relatively simple cool storage systems

that are easier to design and operate, but

should ensure that facility staff are properly trained on the operation and maintenance of cool storage systems.

The Technology’s Development

Cool storage is not a new concept; in

fact, its first use came in the 1940s

shortly after the development of vapor

compression cooling systems (Knebel

1995; Hasnain 1998). Early usage was

focused on applications with exceptionally high ratios of peak to average

cooling demand, such as in theaters,

churches, arenas, and dairies. Ice-on-coil

storage systems were often used with

the principal motivation being to reduce

chiller size. As cooling systems spread to

other building space cooling applications

in the 60s and 70s, cool storage was not

often used, resulting in significant electric load growth concentrated during

the daytime hours of summer. The subsequent low utilization of power generating and delivery assets caused utilities

to offer various incentives promoting

cool storage as well as other demand

management technologies. The result

was a second wave of cool storage

development and use. The development of effective water stratification

technologies made chilled water storage more popular. Ice-on-coil technology improved through the development

of non-metal coils and “packaged” systems. Eutectic salt and encapsulated ice

storage systems were developed to provide latent heat storage alternatives to

ice-on-coil and ice-harvesting technologies. More recent developments include

ice slurry generators and chilled water

systems employing additives to decrease

the minimum storage temperature in

chilled water storage systems.

Technology Outlook

Cool storage technology is approximately 50 years old, but innovations
24

FEDERAL ENERGY MANAGEMENT PROGRAM

continue as indicated by the recent

developments described above. Product innovation is driven by a competitive market (see manufacturers list) and

changing economic conditions. Deregulation of the electric utility industry has

reduced or eliminated many demand

side management programs. As a result,

utility incentives for cool storage are not

as common or generous as they were in

the past. On the other hand, deregulation seems likely to spur electricity pricing structures (e.g., real-time pricing)

that will enhance the need for loadcontrol technologies such as cool storage. On net, the financial benefits of

shifting load to off-peak hours are still

very important, but greater emphasis

is being placed on system designs that

reduce chiller size and cost and/or

improve building system efficiency.

Manufacturers

Cool storage system manufacturers were

identified by combining lists from product directories published by Thomas

Register, Energy Products, Heating/

Piping/Air-Conditioning, Energy User

News, Consulting-Specifying Engineer,

International Thermal Storage Advisory

Council, E-Source, and the International

District Energy Association. We also conducted searches of Internet web sites

and library databases. Each manufacturer was contacted to determine the

type of cool storage equipment offered

and its characteristics.

Despite our efforts, it is practically impossible to ensure that all manufacturers of

cool storage equipment have been identified. To those, we extend our apologies.

This list is provided as a service for

those interested in obtaining information on specific cool storage products.

No endorsement or other judgment

regarding qualification of any manufacturer listed is given or implied.

Applied Thermal Technologies

Hydro-Miser Division

906-B Boardwalk

San Marcos, CA 92069

Phone: 760-744-5031

Fax: 760-744-5031

Principal TES Product: chiller integrated

with external-melt, ice-on-coil storage

Baltimore Aircoil Company

7595 Montivides Road

Jessup, MD 20794

Phone: 410-799-6200

Fax: 410-799-6416

Principal TES Products: chiller integrated

with internal-melt, ice-on-coil storage

for rooftop HVAC retrofit; external-melt,

ice-on-coil storage; ice-on-coil tube bundles

Berg Chilling Systems, Inc.

51 Nantucket Blvd.

Toronto, ON, Canada M1P 2N5

Contact: Walter Langille

Phone: 416-755-2221

Fax: 416-755-3874

www.berg-group.com

Principal TES Product: chiller integrated

with ice harvester

Caldwell Energy and Environmental, Inc.

4000 Tower Road

Louisville, KY 40219

Contact: Drew Wozniak

Phone: 502-964-6450

Fax: 502-966-8732

Principal TES Products: chiller integrated

with ice harvester; chilled water or ice/

water storage tanks; external-melt, iceon-coil storage

Calmac Manufacturing Corporation

101 West Sheffield Ave.

P.O. Box 710

Englewood, NJ 07631-0710

Contact: Roy Nathan

Phone: 201-569-0420

Fax: 201-569-7593

www.calmac.com

Principal TES Products: internal-melt,

ice-on-coil storage; internal-melt, ice-oncoil storage for rooftop HVAC retrofit

Chester-Jensen Company, Inc.

P.O. Box 908

Chester, PA 19016

Contact: Steve Miller

Phone: 610-876-6276

Fax: 610-876-0485

Principal TES Product: external-melt,

ice-on-coil storage

Chicago Bridge and Iron Company

601 W. 143rd Street, P.O. Box 9

Plainfield, IL 60544-0009

Contact: Rich Horn

Phone: 815439-3100

Fax: 815-439-3130

www.chicago-bridge.com

Principal TES Product: chilled water

storage tank

Cristopia Energy Systems

165 Via Catarina

San Dimas,CA 91773

Contact: Moudood A. Aslam

Phone: 909-305-0463

Fax: 909-305-0463

Principal TES Product: eutectic salt latent

heat storage systems

Cryogel

P.O. Box 910525

San Diego, CA 92191

Contact: Bruce McDavid

Phone: 619-792-9003

Fax: 619-792-2743

Principal TES Product: encapsulated

water/ice storage balls

Dunham-Bush

101 Burgess Road

Harrisonburg, VA 22801

Contact: Nathan Hathaway

Phone: 540-434-0711

Fax: 540-434-4595

www.dunham-bush.com

Principal TES Product: chiller integrated

with internal-melt, ice-on-coil storage

Evapco, Inc.

P.O. Box 1300

Westminster, MD 21158-0399

Contact: Craig Goralski

Phone: 410-756-2600

Fax: 410-756-6450

Principal TES Product: external-melt

ice-on-coil storage
25

FEDERAL ENERGY MANAGEMENT PROGRAM

FAFCO, Inc.

2690 Middlefield Road

Redwood City, CA 94063-3455

Contact: Tyler Bradshaw

Phone: 650-363-2752

Fax: 650-363-8423

www.fafco.com

Principal TES Product: internal-melt,

ice-on-coil storage

Girton Manufacturing Company, Inc.

P.O Box 900 TR

Millville, PA 17846-0900

Contact: Rich Puterbaugh

Phone: 570-458-5521

Fax: 570-458-5589

Principal TES Product: chiller integrated

with external-melt, ice-on-coil storage;

external-melt, ice-on-coil storage

Integrated Ice Systems Inc.

Woodinville, WA

Contact: R.A. Roland

Phone: 425-488-1877

Principal TES Product: chiller integrated

with internal-melt, ice-on-coil storage

Matrix Service, Inc.

San Luis Tank Division

825 26th Street, P.O. Box 245

Paso Robles, CA 93447-0245

Contact: Lorin Todd

Phone: 805-238-0888

Fax: 805-238-2724

Principal TES Product: chilled water

storage tank

Morris and Associates

P.O. Box 1046

Raleigh, NC 27602

Contact: Dan Caswell

Phone: 919-779-1250

Fax: 919-779-3466

Principal TES Product: chiller integrated

with ice harvester

Paul Mueller Company

1600 W. Phelps, P.O. Box 828

Springfield, MO 65801-0828

Contact: Duke Gault

Phone: 417-831-3000

Fax: 417-862-9008

www.muel.com

Principal TES Product: ice slurry generator

Natgun Corporation

Contact: Chris Hodgson

Phone: 800-662-8486

Principal TES Product: chilled water

storage tank

North Star Ice Equipment Corporation

P.O. Box 80227

Seattle, WA 98108-0227

Phone: 800-959-0875

Fax: 206-763-7323

Principal TES Product: chiller integrated

with ice harvester

Pitt-DesMoines, Inc.

3400 Grand Ave.

Pittsburgh, PA 15225

Contact: Gary Wildman

Phone: 412-331-3000

Fax: 412-331-3188

Principal TES Product: chilled water

storage tank

Preload, Inc.

5710 LBJ Freeway, Suite 140

Dallas, TX 75240

Contact: Bill Devitt

Phone: 972-385-0550

Fax: 972-385-0557

www.preload.com

Principal TES Product: chilled water

storage tank

Powell Energy Products, Inc.

3041 Home Road, P.O Box 203

Powell, OH 43065-0203

Contact: Michael McRell

Phone: 614-881-5596

Fax: 614-881-5989

Principal TES Product: internal-melt, iceon-coil storage for rooftop HVAC retrofit

Sunwell Technologies, Inc.

180 Caster Ave.

Woodbridge, ON, Canada L4L 5Y7

Contact: Jamie-Lee Wilson

Phone: 905-856-0400

Fax: 905-856-1935

www.sunwell.com

Principal TES Product: ice slurry generator

Tampa Tank, Inc.

5205 Adamo Drive

Tampa, FL 33619

Contact: Jim Daniels

Phone: 813-623-2675

Fax: 813-626-1641

www.tampatank.com

Principal TES Product: chilled water

storage tank

Thermal Technologies, Inc.

1827 Wehrli Road, Suite 105

Naperville, IL 60565

Contact: John Andrepont

Phone: 630-357-2666

Fax: 630-527-2349

Principal TES Product: chilled water

storage tank with chemical additives to

allow lower temperature storage

Trane Company

3600 Pammel Creek Road

La Crosse, WI 54601

Phone: 608-787-2000

www.trane.com

Principal TES Product: internal-melt,

ice-on-coil storage

Waffle-Crete International, Inc.

2500 East 9th Street Road, P.O. Box 1008

Hays, KS 67601

Contact: Linda McLain

Phone: 785-625-3486

Fax: 785-625-8542

www.waffle-crete.com

Principal TES Product: chilled water

storage tank

Who is Using the Technology

Thousands of cool storage systems have

been installed in the United States. A

survey conducted for ASHRAE resulted

in an estimated population of 1500–2000

systems in the early 1990s (Potter 1994).

The vast majority of these systems have

been installed in non-Federal facilities.

Applications cover a wide range of

facility types, but most commonly are

offices, schools, retail stores, places of

worship, refrigerated food storage facilities, and hospitals.
26

FEDERAL ENERGY MANAGEMENT PROGRAM

Between 80% and 85% of the systems

installed use one of the several kinds of

ice storage. Another 10–15% use chilled

water storage, with eutectic salt systems

representing about 5% of the systems in

the survey conducted by Potter (1994).

Based on data collected from cool storage equipment manufacturers for this

FTA, only about 1% of the systems

have been installed at Federal facilities.

Selected Federal sites using cool storage

systems are identified below.

Moorhead Federal Building

1000 Liberty Avenue

Pittsburgh, PA 15222

Jerry Bower, Maintenance and

 Operations Foreman

412-395-5436

Ralph H. Johnson VA Medical Center

Charleston, SC

Jim Brennen, Energy Manager

843-577-5011 ext. 7229

Dallas VA Medical Center

4500 S. Lancaster Road

Dallas, TX 75216

Larry Stevenson, Energy Manager

214-372-7020

Brookhaven National Laboratory

Building 134 C

Upton, NY 11973

Mark Toscana, Energy Manager

516-344-2599

Sandia National Laboratories

Albuquerque, NM

Gerald Savage, Construction

 Management Engineer

505-844-9403

U.S. Army Reserve Center

9825 Garden Road

Monclova, OH 43542

Gary Smith, Facility Manager

419-868-3921 ext. 109

For Further Information

Associations

Air Conditioning and Refrigeration

Institute

4301 North Fairfax Drive, Suite 425

Arlington, VA 22203

Phone: 703-524-8800

Fax: 703-528-3816

www.ari.org

American Society of Heating,

Refrigeration, and Air Conditioning

Engineers

1791 Tullie Circle

Atlanta, GA 30329

Phone: 404-636-8400

Fax: 404-321-5478

www.ashrae.org

Electric Power Research Institute

3412 Hillview Avenue, P.O. Box 10412

Palo Alto, CA 94303

Phone: (650) 855-2000

Fax: (650) 855-2263

www.epri.com

HVAC&R Center

150 East Gilman Street, Suite 2200

Madison, WI 53703

Phone: 800-858-3774

Fax: 608-262-6209

www.engr.wisc.edu/centers/tsarc/

tsarc.html

International District Energy Association

1200 19th Street, N.W. Suite 300

Washington, D.C. 20036-2412

Phone 202-429-5111

Fax: 202-429-5113

www.energy.rochester.edu/idea/

Design and Installation Guides

Design Guide for Cool Thermal Storage

American Society of Heating, Refrigeration, and Air Conditioning Engineers

1791 Tullie Circle

Atlanta, Georgia 30329

Study of Operational Experience with

Thermal Storage Systems

American Society of Heating, Refrigeration, and Air Conditioning Engineers

1791 Tullie Circle

Atlanta, Georgia 30329

Successful Cool Storage Projects: From

Planning to Operation

American Society of Heating, Refrigeration, and Air Conditioning Engineers

1791 Tullie Circle

Atlanta, Georgia 30329

Source Energy and Environmental Impacts

of Thermal Energy Storage

California Energy Commission

1516 Ninth Street

Sacramento, CA 95814-5504

Commercial Space Cooling and Air

Handling Technology Atlas Cool Thermal

Storage Chapter

E SOURCE, Inc.

4755 Walnut Street

Boulder, Colorado 80301-2537

References

Ahlgren, R.M. 1987. Water Treatment

Technologies for Thermal Storage

Systems. EPRI EM-5545. Electric Power

Research Institute. Palo Alto, California.

ASHRAE. 1997. ASHRAE Handbook –

Fundamentals . American Society of

Heating, Refrigeration, and Air Conditioning Engineers. Atlanta, Georgia.

ASHRAE. 1993. Design Guide for Cool

Thermal Storage. American Society of

Heating, Refrigeration, and Air Conditioning Engineers. Atlanta, Georgia.

Bahnfleth, W.P. and W.S. Joyce. 1995.

“Stratified Storage Economically

Increases Capacity and Efficiency

of Campus Chilled Water System.”

ASHRAE Journal (March, 1995).

Caldwell, J.S. and W.P. Bahnbleth. 1997.

“Chilled Water Thermal Energy Storage

without Electric Rate Incentives or

Rebates.” Journal of Architectural

Engineering (September, 1997).
27

FEDERAL ENERGY MANAGEMENT PROGRAM

Cahners Business Information. 1999.

Energy User News. Vol. 24, No. 5.

Cahners Business Information. 1999b.

Energy User News. Vol. 24, No. 8.

Duffy, G. 1992. “Thermal Storage

Emphasis Shifts to Saving Energy.”

Engineered Systems (July/August, 1992).

Electric Power Research Institute. 1992.

Water-Thermal Energy Storage Fact Sheet.

Palo Alto, California.

E Source, Inc. 1998. Commercial Space

Cooling and Air Handling Technology

Atlas; Cool Thermal Storage Chapter.

Boulder, Colorado.

Hasnain, S.M. 1998. “Review on Sustainable Thermal Energy Storage Technologies, Part II: Cool Thermal Storage. Energy

Conversion Management. Vol. 39, No. 11.

Knebel, D.E. 1995. “Current Trends in

Thermal Storage.” Engineered Systems

(January, 1995).

MacCracken, C.D. 1993. “Off-peak air

conditioning: A major energy saver.”

ASHRAE Journal (May 1993).

MacCracken, C.D. 1994. “Cold Air

Systems: Sleeping Giant.” Heating/

Piping/Air Conditioning (April 1994).

Means, R.S. Company. 1999. Mechanical

Cost Data 1999. Kingston, Massachusetts.

Potter, R.A. 1994. Study of the Operational

Experience with Thermal Storage Systems.

ASHRAE Research Project 766. American

Society of Heating, Refrigeration, and Air

Conditioning Engineers. Atlanta, Georgia.

Sohn, C.W. and G.L. Cler. 1990. “Assessment of Market Potential in Storage

Cooling Systems for Army Facilities.”

ASHRAE Transactions, Vol. 96, Part 1.

Strutz, M.J. 1995. “Chilled water storage:

It’s more than just shedding peaks.”

Proceedings, 86th Annual Conference

of the International District Energy

Association. Washington, D.C.
28

FEDERAL ENERGY MANAGEMENT PROGRAM

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29

FEDERAL ENERGY MANAGEMENT PROGRAM

Appendixes

Appendix A: Federal Life-Cycle Costing Procedures and the BLCC Software

Appendix B: QuickBLCC Results for Case Study
30

FEDERAL ENERGY MANAGEMENT PROGRAM

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31

FEDERAL ENERGY MANAGEMENT PROGRAM

Appendix A

Federal Life-Cycle Costing Procedures and the BLCC Software

Federal agencies are required to evaluate energy-related investments on the basis of minimum life-cycle costs (10 CFR Part 436).

A life-cycle cost evaluation computes the total long-run costs of a number of potential actions, and selects the action that minimizes the long-run costs. When considering retrofits, sticking with the existing equipment is one potential action, often called the

baseline condition. The life-cycle cost (LCC) of a potential investment is the present value of all of the costs associated with the

investment over time.

The first step in calculating the LCC is the identification of the costs. Installed Cost includes cost of materials purchased and the

labor required to install them (for example, the price of an energy-efficient lighting fixture, plus cost of labor to install it).

Energy Cost includes annual expenditures on energy to operate equipment. (For example, a lighting fixture that draws 100 watts

and operates 2,000 hours annually requires 200,000 watt-hours (200 kWh) annually. At an electricity price of $0.10 per kWh,

this fixture has an annual energy cost of $20.) Nonfuel Operations and Maintenance includes annual expenditures on parts and

activities required to operate equipment (for example, replacing burned out light bulbs). Replacement Costs include expenditures

to replace equipment upon failure (for example, replacing an oil furnace when it is no longer usable).

Because LCC includes the cost of money, periodic and aperiodic maintenance (O&M) and equipment replacement costs,

energy escalation rates, and salvage value, it is usually expressed as a present value, which is evaluated by

LCC = PV(IC) + PV(EC) + PV(OM) + PV(REP)

where PV(x) denotes “present value of cost stream x,”

IC is the installed cost,

EC is the annual energy cost,

OM is the annual nonenergy O&M cost, and

REP is the future replacement cost.

Net present value (NPV) is the difference between the LCCs of two investment alternatives, e.g., the LCC of an energy-saving

or energy-cost-reducing alternative and the LCC of the existing, or baseline, equipment. If the alternative’s LCC is less than the

baseline’s LCC, the alternative is said to have a positive NPV, i.e., it is cost-effective. NPV is thus given by

NPV = PV(EC0) – PV(EC1)) + PV(OM0) – PV(OM1)) + PV(REP0) – PV(REP1)) – PV(IC)

or

NPV = PV(ECS) + PV(OMS) + PV(REPS) – PV(IC)

where subscript 0 denotes the existing or baseline condition,

subscript 1 denotes the energy cost saving measure,

IC is the installation cost of the alternative (note that the IC of the baseline is assumed zero),

ECS is the annual energy cost savings,

OMS is the annual nonenergy O&M savings, and

REPS is the future replacement savings.

Levelized energy cost (LEC) is the break-even energy price (blended) at which a conservation, efficiency, renewable, or fuelswitching measure becomes cost-effective (NPV >= 0). Thus, a project’s LEC is given by

PV(LEC*EUS) = PV(OMS) + PV(REPS) – PV(IC)

where EUS is the annual energy use savings (energy units/yr). Savings-to-investment ratio (SIR) is the total (PV) savings of a measure divided by its installation cost:

SIR = (PV(ECS) + PV(OMS) + PV(REPS))/PV(IC).

Some of the tedious effort of life-cycle cost calculations can be avoided by using the Building Life-Cycle Cost software, BLCC,

developed by NIST. For copies of BLCC, call the FEMP Help Desk at (800) 363-3732.
32

FEDERAL ENERGY MANAGEMENT PROGRAM

Appendix B

QuickBLCC Results for Case Study

QuickBLCC (QBLCC 2.7-00) 06-30-2000/11:38:42

QBLCC filename = COOLSTOR.QI

Analysis type = Federal Analysis—Energy Conservation Projects

Project name = Cool Storage Case Study

Base date of study = 2000

Service date = 2000

Study period = 20 years

Discount rate = 3.4%

Annually recurring costs and energy costs discounted from end of year.

Number of alternatives in file = 2

Number of groups in file = 1

Note: Project alternatives displayed in increasing order of investment cost

Group code: Present-Value Costs

Alternative Investment OM&R Energy Total LifeName Costs* Costs Costs Cycle Costs

Conventional $0 $12047177 $0 $12047177

Cool Storage $1600000 $0 $0 $1600000<—MIN LCC

Comparative measures are only calculated for the alternative with lowest

LCC relative to alternative with the lowest present-value investment cost.

Comparative economic measures for Cool Storage relative to Conventional:

NET SAVINGS = $10447177; SIR = 7.53; AIRR = 14.38%

Ratio of present-value energy savings to total savings = 0.00

* Investment costs include capital replacements (if any).

 Residual values are not calculated.
FEDERAL ENERGY MANAGEMENT PROGRAM

About FEMP’s New Technology Demonstration Program

The Energy Policy Act of 1992, and subsequent Executive Orders, mandate that

energy consumption in Federal buildings be reduced by 35% from 1985 levels

by the year 2010. To achieve this goal,

the U.S. Department of Energy’s Federal

Energy Management Program (FEMP)

is sponsoring a series of programs to

reduce energy consumption at Federal

installations nationwide. One of these

programs, the New Technology Demonstration Program (NTDP), is tasked to

accelerate the introduction of energyefficient and renewable technologies

into the Federal sector and to improve

the rate of technology transfer.

As part of this effort FEMP is sponsoring a series of publications that are

designed to disemminate information

on new and emerging technologies.

New Technology Demonstration

Program publications comprise three

separate series:

Federal Technology Alerts—longer

summary reports that provide details

on energy-efficient, water-conserving,

and renewable-energy technologies

that have been selected for further

study for possible implementation in

the Federal sector. Additional information on Federal Technology Alerts (FTAs)

is provided in the next column.

Technology Installation Reviews—

concise reports describing a new technology and providing case study results,

typically from another demonstration

program or pilot project.

Technology Focuses—brief information

on new, energy-efficient, environmentally friendly technologies of potential

interest to the Federal sector.

More on FTAs

Federal Technology Alerts, our signature

reports, provide summary information

on candidate energy-saving technologies developed and manufactured in the

United States. The technologies featured

in the FTAs have already entered the

market and have some experience but are

not in general use in the Federal sector.

The goal of the FTAs is to improve the

rate of technology transfer of new

energy-saving technologies within the

Federal sector and to provide the right

people in the field with accurate, up-todate information on the new technologies so that they can make educated

judgments on whether the technologies

are suitable for their Federal sites.

The information in the FTAs typically

includes a description of the candidate

technology; the results of its screening

tests; a description of its performance,

applications and field experience to date;

a list of manufacturers; and important

contact information. Attached appendixes provide supplemental information and example worksheets on the

technology.

FEMP sponsors publication of the FTAs

to facilitate information-sharing between

manufacturers and government staff.

While the technology featured promises

significant Federal-sector savings, the

FTAs do not constitute FEMP’s endorsement of a particular product, as FEMP

has not independently verified performance data provided by manufacturers.

Nor do the FTAs attempt to chart market

activity vis-a-vis the technology featured.

Readers should note the publication date

on the back cover, and consider the FTAs

as an accurate picture of the technology

and its performance at the time of publication. Product innovations and the

entrance of new manufacturers or suppliers should be anticipated since the

date of publication. FEMP encourages

interested Federal energy and facility

managers to contact the manufacturers

and other Federal sites directly, and to

use the worksheets in the FTAs to aid

in their purchasing decisions.

Federal Energy Management Program

The Federal Government is the largest energy consumer in the nation. Annually, in its 500,000 buildings and 8,000 locations worldwide, it uses nearly two quadrillion Btu (quads) of energy, costing over $8 billion. This represents 2.5% of all

primary energy consumption in the United States. The Federal Energy Management Program was established in 1974 to

provide direction, guidance, and assistance to Federal agencies in planning and implementing energy management programs that will improve the energy efficiency and fuel flexibility of the Federal infrastructure.

Over the years several Federal laws and Executive Orders have shaped FEMP's mission. These include the Energy Policy

and Conservation Act of 1975; the National Energy Conservation and Policy Act of 1978; the Federal Energy Management

Improvement Act of 1988; and, most recently, Executive Order 12759 in 1991, the National Energy Policy Act of 1992

(EPACT), Executive Order 12902 in 1994, and Executive Order 13123 in 1999.

FEMP is currently involved in a wide range of energy-assessment activities, including conducting New Technology

Demonstrations, to hasten the penetration of energy-efficient technologies into the Federal marketplace.
FEDERAL ENERGY MANAGEMENT PROGRAM

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For More Information

FEMP Help Desk

 (800) 363-3732

International callers please use

 (703) 287-8391

Web site: www.eren.doe.gov/femp

General Contacts

Ted Collins

New Technology Demonstration

 Program Manager

Federal Energy Management

 Program

U.S. Department of Energy

1000 Independence Ave., SW, EE-92

Washington, D.C. 20585

Phone: (202) 586-8017

Fax: (202) 586-3000

theodore.collins@ee.doe.gov

Steven A. Parker

Pacific Northwest National

 Laboratory

P.O. Box 999, MSIN: K5-08

Richland, WA 99352

Phone: (509) 375-6366

Fax: (509) 375-3614

steven.parker@pnl.gov

Technical Contact

Daryl R. Brown

Pacific Northwest National

 Laboratory

P.O. Box 999, MSIN: K8-07

Richland, WA 99352

Phone: (509) 372-4366

Fax: (509) 372-4370

daryl.brown@pnl.gov

Produced for the U.S. Department

of Energy by the Pacific Northwest

National Laboratory

DOE/EE-0241

December 2000

Log on to FEMP’s New Technology Demonstration Program

Website

http://www.eren.doe.gov/femp/prodtech/newtechdemo.html

You will find links to

• An overview of the New Technology Demonstration Program

• Information on the program’s technology demonstrations

• Downloadable versions of program publications in Adobe Portable

Document Formats (pdf)

• A list of new technology projects underway

• Electronic access to the program’s regular mailing list for new products

when they become available

• How Federal agencies may submit requests for the program to assess

new and emerging technologies