PNNL-14836 

Analysis of IECC2003 Chiller Heat Recovery 

for Service Water Heating Requirement for 

New York State 

D. W. Winiarski 

August 2004 

Prepared for the 

U.S. Department of Energy 

Office of Building Technologies 

under Contract DE-AC06-76RL01830 
DISCLAIMER 

This report was prepared as an account of work sponsored by an 

agency of the United States Government. Neither the United States 

Government nor any agency thereof, nor Battelle Memorial Institute, 

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, trademark, 

manufacturer, or otherwise does not necessarily constitute or imply its 

endorsement, recommendation, or favoring by the United States 

Government or any agency thereof, or Battelle Memorial Institute. The 

views and opinions of authors expressed herein do not necessarily state 

or reflect those of the United States Government or any agency thereof. 

PACIFIC NORTHWEST NATIONAL LABORATORY 

operated by

BATTELLE 

for the

UNITED STATES DEPARTMENT OF ENERGY 

under Contract DE-AC06-76RL01830

Printed in the United States of America

Available to DOE and DOE contractors from the 

Office of Scientific and Technical Information, 

P.O. Box 62, Oak Ridge, TN 37831-0062; 

ph: (865) 576-8401 

fax: (865) 576-5728 

email: reports@adonis.osti.gov 

Available to the public from the National Technical Information Service, 

U.S. Department of Commerce, 5285 Port Royal Rd., Springfield, VA 22161 

ph: (800) 553-6847 

fax: (703) 605-6900 

email: orders@ntis.fedworld.gov 

online ordering: http://www.ntis.gov/ordering.htm 

This document was printed on recycled paper.

(8/00)
Analysis of IECC2003 Chiller Heat Recovery for 

Service Water Heating Requirement for 

New York State 

D. W. Winiarski 

August 2004 

Prepared for 

the U.S. Department of Energy 

Office of Building Technologies 

under Contract DE-AC06-76RL01830 

Pacific Northwest National Laboratory 

Richland, Washington 99352 

iii 

Summary 

The state of New York asked the U.S. Department of Energy to evaluate the cost-effectiveness of the 

requirement for heat recovery for service water heating that exists in the 2003 International Energy 

Conservation Code to determine whether this requirement should be adopted into the New York State 

Energy Code. A typical hotel application that would trigger this requirement was examined using whole 

building simulation software to generate baseline annual chiller and service hot water loads, and a 

spreadsheet was used to examine the energy savings potential for heat recovery using hourly load files 

from the simulation. An example application meeting the code requirement was developed, and the 

energy savings, energy cost savings, and first costs for the heat recovery installation were developed. The 

calculated payback for this application was 6.3 years using 2002 New York state average energy costs. 

This payback met the minimum requirements for cost effectiveness established for the state of New York 

for updating the commercial energy conservation code. 
iv 

Table of Contents 

Summary ................................................................................................ iii

Background ..............................................................................................v

Applicable Buildings ...............................................................................2

Analysis Methodology .............................................................................6

Development of DOE2.2 Building Model..............................................................6 

Development of Service Hot Water Load Estimates..............................................8 

Base Building Simulation......................................................................10

Condenser Heat Rejection and Service Hot Water Loads................................... 12 

Heat Recovery Strategy ....................................................................................... 12 

Impact on Chiller Performance............................................................................ 14 

Impacts to Heat Rejection Equipment ................................................................. 14 

Energy Cost Savings............................................................................................ 14 

Installed Cost ....................................................................................................... 15 

Estimated Payback............................................................................................... 15

Conclusion ..............................................................................................16

References ..............................................................................................17

Appendix A Design Parameters for Plate Heat Exchanger.............20

Appendix B Estimated Costs for Heat Recovery System..................23
 v 

Figures

 1. Hot Water Load Profile from DOE2.2, Hotel.........................................................................................8

 2. Electrical Energy Consumption for Base Hotel Building, by End Use. ................................................10

 3. Natural Gas Energy Consumption for Base Hotel Building, by End Use..............................................11

 4. Schematic of Service Heat Recovery System .......................................................................................13

Tables 

 1. Aggregate Number of Building and Represented Floor Space for Buildings Operated 24 Hours per 

Day and Using Central Chillers (CBECS 1995)...................................................................................3

 2. Minimum Cooled Floor Area for a Building with 400 tons of Cooling. ..............................................3

 3. Fraction of Remaining Buildings with Cooled Space > 100,000 ft2.....................................................4

 4. Estimate of Building Size for a 1,000,000 Btu/h Service Hot Water Load ..........................................5

 5. Building Simulation Model Details ......................................................................................................7

 6 Energy Consumption for Base Hotel Building, by End Use................................................................11

 7. Building Energy Impacts from Heat Recovery...................................................................................15

A-1. Design Parameters for Plate Heat Exchanger Systems (Haselego) ....................................................20 

A-2. Final Double-Wall-Vented Plate Heat Exchanger Specification Sheet used in Energy Savings .......21 

B-1. Material, Labor, and Total Estimated Installation Cost for Heat Recovery System...........................23 
1 

Background 

The state of New York requested the U.S. Department of Energy evaluate the cost effectiveness of the 

requirement for condenser heat recovery for service water heating that exists in the 2003 version of the 

International Energy Conservation Code (IECC 2003) (herein referred to as IECC2003) using the 10-year 

payback economic criteria for the state of New York. 

The heat recovery for service water heating requirement in the IECC2003 stems from a nearly identical 

requirement that exists in ANSI/ASHRAE/IESNA 90.1-2001 (ASHRAE 90.1-2001) as well as its 

predecessor, ANSI/ASHRAE/IESNA 90.1-1999 (ASHRAE 90.1-1999). The requirement is designed to 

encourage the use of condenser heat recovery from water-cooled air conditioning systems when a 

significant service water heating load exists that could benefit from the recovered heat. The IECC2003 

requirement is shown below. 

803.3.9 Heat Recovery for Service Water Heating. Condenser heat recovery systems shall be 

installed for heating or reheating of service hot water provided that the facility operates 24 hours a 

day, the total installed heat rejection capacity of water-cooled systems exceeds 6,000,000 Btu/h of 

heat rejection, and the design service water heating load exceeds 1,000,000 Btu/h. 

The required heat recovery system shall have the capacity to provide the smaller of: 

1) Sixty percent of the peak heat rejection load at design conditions; or 

2) The preheating required to raise the peak service hot water draw to 85°F (29°C). 

Exceptions:

(a) Facilities that employ condenser heat recovery for space heating or reheat purposes with a heat 

recovery design exceeding 30 percent of the peak water-cooled condenser load at design 

conditions. 

(b) Facilities that provide 60% of their service water heating from site solar or site recovered energy 

or from other sources. 

This document contains a limited analysis of the cost-effectiveness of this requirement based on a 

“typical” application in the state of New York. Because of the huge potential variation in building 

designs and uses for buildings with the characteristics defined above, no attempt is made to ensure that 

the requirement would always be cost effective, but rather to indicate whether or not a cost-effective 

implementation exists in a “typical” application that meets the above criteria. 
2 

Applicable Buildings 

The trigger criteria for this requirement are based on building hours of operation, total installed heat 

rejection capacity of water-cooled systems, and design service water heating load. The combination of 

these three items can be used to identify typical building applications. To identify the characteristic 

buildings for this study, the three criteria were applied to the 1995 Commercial Building Energy 

Consumption Survey (CBECS) building data set (EIA 1997), as described below, to subset that building 

sample to identify the “typical” applications in the U.S. 

The first criterion examined is the requirement for 24-hour operation. While any commercial building 

can be used on a 24-hour basis, the most common buildings were expected to be hotel/motel, multifamily 

housing, inpatient health care (e.g., hospitals), some laboratories and industrial facilities, refrigerated 

warehouse, and some large retail buildings. In the subsetting of the CBECS data set, only buildings that 

reported 24 hour-a-day operation were examined (weekly hours of operation variable WKHRS6 in 

CBECS was equal to 168). This reduced the original building sample from 5766 buildings to 1103 

buildings. 

The second requirement is that they have over 6,000,000 Btu/h of heat rejection capacity of the watercooled systems. Approximately 15,000 Btu/h of heat is rejected per ton of cooling, so this indicates total 

cooling capacity near 400 tons. In most cases, this will indicate relatively large water-cooled chiller 

systems providing the available cooling for the building. The CBECS sample selection was further subset 

to include only buildings that reported the use of central chillers (CBECS Variable CHILLR6 equals 1). 

This further reduced the sample to 361 buildings encompassing a variety of building “types” [technically 

the “Principle Building Activity” (PBA) classification] used by CBECS. The number of buildings and 

total square footage of buildings by PBA is shown in Table 1. 

The requirement for over approximately 400 tons of cooling was used to further subset the database. The 

minimum total capacity of a water-cooled system helps to identify the minimum building area that should 

be cooled by chillers in the building. To make use of this data, estimates of typical building square 

footage served per ton of cooling are used (Bell 2000). Because these are simply design rules of thumb, 

and may not be indicative of current or future new design, it is recognized that this will only provide an 

approximate building size estimate. However, this is expected to remove a large portion of the buildings, 

which would clearly be too small to engage the current IECC2003 heat recovery for service water heating 

requirement. 

Table 2 shows the typical cooling intensities assumed by building type for the majority of buildings types 

shown in Table 1, as well as providing the approximate minimum building size that would be served by a 

400-ton or larger cooling system using the sizing rules of thumb shown by Bell (Bell 2000). As can be 

seen, most buildings will be close to 100,000 ft2

 of cooled space before they are likely to require 400 tons 

of cooling capacity. For the purposes of this study, we subset the CBECS data further by requiring at 

least 100,000 ft2

 of building area be cooled in the sample. 
 3 

Table 1. Aggregate Number of Building and Represented Floor Space for Buildings Operated 24 

Hours per Day and Using Central Chillers [EIA 1997 (CBECS data 1995)] 

Principal building activity Number of Buildings Represented Floor 

Space (sf) 

Education 8 107985564 

Enclosed shopping center/Mall 1 8304000 

Food services (restaurants) 1 4152000 

Health care (inpatient) 136 1210545179 

Health care (outpatient) 6 27501650 

Laboratory 4 27490275 

Lodging (hotel/motel/dorm) 51 725700449 

Nursing home 8 97075113 

Office/Professional 95 757412437 

Other 2 80215500 

Public assembly 11 220030250 

Public order and safety 13 169349926 

Retail (except mall) 1 5868000 

Service (except food) 10 230147400 

Strip shopping 1 16118400 

Vacant 5 66577075 

Warehouse (non-refrigerated) 8 118103514 

Grand Total 361 3872576731 

Table 2. Minimum Cooled Floor Area for a Building with 400 tons of Cooling. 

Building Type Bell Classification sf/ton Area Served by 400 

Ton Cooling 

System (SF) 

Education 6.16 School Classrooms 250 100000

Enclosed shopping 

center/Mall 

6.22 Malls 250 100000

Food services (restaurants) 6.17 Dining Halls, Lunch Rooms 175 70000

Health care (inpatient) 6.09 Hospital Patient Rooms 275 110000

Health care (outpatient) 6.11 Medical Dental Centers Clinics 275 110000

Laboratory 6.10 100% OA Labs 200 80000

Lodging (hotel/motel/dorm) 6.14 Motel/Hotel Public Spaces and 

6.15 Motel/Hotel Guestrooms 

363 145000

Nursing home 6.09 Hospital Patient Rooms 275 110000

Office/Professional 6.01 Offices, Commercial 350 140000

Other 6.27 All Spaces (low range estimate) 300 120000

Public assembly 6.18 Libraries/Museums 300 120000

Public order and safety 6.03, Police Stations 300 120000

Retail (except mall) 6.19 Retail Department Stores 250 100000

Identification of remaining subset of the CBECS 95 buildings, where the cooled building area is greater 

than 100,000 ft2

, results in the data shown in Table 3. 
 4 

Table 3. Fraction of Remaining Buildings with Cooled Space > 100,000 ft2

Principal building activity Count of 

CBECS 

buildings 

greater than 

100,000 ft2

Fraction of 

Remaining 

Sample 

Represented 

Floor Space 

(ft2

) 

Fraction of 

Represented 

Floor Space 

Education 6 2.2% 47185564 1.61%

Enclosed shopping 

center/Mall 

1 0.4% 8304000

0.28%

Food services (restaurants) 1 0.4% 4152000 0.14%

Health care (inpatient) 112 41.8% 1017163997 34.68%

Health care (outpatient) 3 1.1% 16687000 0.57%

Laboratory 2 0.7% 14532000 0.50%

Lodging (hotel/motel/dorm) 33 12.3% 541006577 18.45%

Nursing home 2 0.7% 52623400 1.79%

Office/Professional 76 28.4% 587328037 20.03%

Other 2 0.7% 80215500 2.73%

Public assembly 5 1.9% 103274300 3.52%

Public order and safety 5 1.9% 91004850 3.10%

Retail (except mall) 1 0.4% 5868000 0.20%

Service (except food) 8 3.0% 199205250 6.79%

Strip shopping 0 0.0% 0 0.00%

Vacant 4 1.5% 57733000 1.97%

Warehouse (nonrefrigerated) 7 2.6% 106651414

3.64%

Grand Total 268 100.0% 2932934889 100.00%

As can be seen, the majority of the floor space in the remaining building sample is in three categories: 

Office/Professional, Inpatient Health Care, and Lodging. 

Finally, it is important to consider the size of the water heating system in these buildings. The water 

heating system is required to have a peak size of 1,000,000 Btu/h for the requirement to be in effect. An 

estimate of the size of building for which this load exists can be made by looking at the typical service hot 

water (SHW) peak flows and temperature rise. The ASHRAE 1999 Applications Handbook (ASHRAE 

1999) provides some useful data for office buildings and motel/hotel applications. Office buildings are 

reported to have maximum hourly use rates averaging 0.4 gal/person. Large motels (100 or more units) 

typically report maximum hourly usage of 4 gal/guestroom for personal water consumption. Food 

service, laundry, or hot water provided for pool heating are not included in this motel number. Laundry, 

while a significant hotel hot water load, is commonly done in the middle of the day or after checkout time 

and may be largely ignored in determining peak water consumption (George 2003, Meyer 2001). 

The ASHRAE data can be thought of in terms of service units, where the service units in these examples 

are number of persons or number of guestrooms to be served by the water heating system. To determine 

the peak hot water load per square foot, we need to establish the number of service units per square foot. 

An example of how this is done is provided in DOE’s Screening Analysis for EPACT Covered 

Commercial HVAC and Water Heating Equipment (DOE 2000) for several building types. Table 4 
 5 

shows service unit density, and subsequent water load for office and hotel buildings. A low inlet water 

temperature of 40°F and tank water temperature of 140°F were assumed for sizing purposes. The 

building area corresponding to a 1,000,000 Btu/h service water heating load is shown in the last column 

on the right. 

Table 4. Estimate of Building Size for a 1,000,000 Btu/h Service Hot Water Load 

Building type Service Unit 

Service 

Units 

/1000 sf 

Peak SHW 

Flow 

(gal/h per 

service 

unit) 

Peak 

hourly 

SHW Load 

Btu/h/1000 

sf 

Building 

Area/1,000,000 

Btu/h (sf) 

Lodging 

(hotel/motel/dorm) guestrooms 3.3 4 10890 91827

Office/Professional person 3.3 0.4 1089 918274

This data for hotel and offices indicates that a hotel size of approximately 92,000 ft2

 would likely have a 

peak hot water demand of approximately 1,000,000 Btu/h. An office building, even one operated 24 

hours/day, would have to be closer to 920,000 ft2

 in size to have a similar peak hot water load. A 

hospital, while not shown in Table 4, would be expected to have hot water loads similar to, or somewhat 

greater than, that of a lodging facility. 

The analysis suggests that a hotel greater than approximately 100,000 ft2

 in size represents a common 

application of the IECC heat recovery requirement. Inpatient hospitals may be even more common 

applications based on the data presented in Tables 1 through 3. Very large office buildings 

(approximately 1,000,000 ft2

 in size) may also represent buildings where the requirement would be in 

force. However, a review of the CBECS data set suggests that such office buildings would be a smaller 

fraction of the applications. Of the 76 office buildings shown in Table 3 (representing 587 million ft2

 of 

floor space), only 23 buildings were 920,000 ft2

 or bigger (174 million ft2 of floor space). However, 

given New York’s large metropolitan population, it is important to not overlook this building category 

during implementation. 

The remainder of this analysis will focus on application of condenser heat recovery in a large hotel 

building. 
6 

Analysis Methodology 

The analysis methodology here is to: 

1) Develop a simplified model of a building of a size and application that would typically trigger the 

requirement as defined in the IECC2003. 

2) Develop service hot water (SHW) usage and usage profiles for these buildings. 

3) Estimate chiller heat rejection for these buildings based on simulated chiller usage. 

4) Define strategy for chiller heat recovery. 

5) Size heat recovery equipment for each strategy. 

6) Estimate available annual service hot water heating energy avoided through use of heat recovery. 

7) Determine avoided service hot water heating cost resulting from heat recovery. 

8) Determine the impact to chiller performance and chiller electrical usage. 

9) Determine additional operational cost for heat recovery. 

10) Determine the potential for equipment downsizing. 

11) Determine cost premium for heat recovery installation. 

12) Determine simple payback for service hot water heat recovery. 

These steps are outlined in the following pages of the report. Further details may also be found in the 

Appendices. 

Development of DOE2.2 Building Model 

A whole building simulation was created for the hotel building using DOE2.2 (Hirsch 2003). The hotel 

building is composed of two identical hotel wings, each with a total floor area of approximately 100,000 

ft2

, and three stories tall.a The individual wings of the building prototype use five building zones per floor 

consisting of a core zone and four perimeter zones. The area per floor is 33,856 ft2

. Only one wing of the 

building is actually simulated. The building simulated is a simple rectangle in shape, with each floor 368 

ft in length and 52 ft in width. The long axis of the building is oriented east-west. 

The perimeter of the building is assumed to consist largely of individual rooms, approximately 20 ft in 

depth. Envelope and heating, ventilation and air conditioning (HVAC) characteristics were developed 

 

a

 Although rule of thumb cooling load and sizing guidelines suggested a 100,000 ft2 hotel building, initial 

building loads analysis for that size building did not indicate a heat rejection of 6,000,000 Btu/h for this 

location and with the assumed building load assumptions. The building size was then doubled for this 

analysis to be representative of current construction practices. 
 7 

from requirements found in ASHRAE 90.1-2001. ASHRAE 90.1 provides an alternate compliance path 

for in the IECC2003, and it was felt to be more representative of the code used in larger commercial 

buildings. Lighting power densities were developed based on those found in the IECC2003 currently 

being considered for adoption by the state of New York. 

A central plant, consisting of a single screw chiller and central hot water boiler per building wing serve 

the HVAC needs of the building. Individual fan coil units are assumed to serve the individual rooms and 

other spaces. Other building statistics are shown in Table 5, below. 

Table 5. Building Simulation Model Details 

General Building Info 

Building type Hotel 

Floor area 101,568 ft2

Number of stories 3 

Shape Rectangular 

Length 368 ft 

Width 92 ft 

Floor-to-floor height 13 ft 

Floor-to-ceiling height 9 ft 

Window–wall-ratio 30% 

Perimeter area fraction 49.6% 

Core area 50.4% 

Building peak occupancy 551 persons 

Hotel rooms 335 rooms 

Building misc eq. load 0.266 Btu/h-ft2

Envelope Characteristics 

Wall type Mass 

Wall U-factor 0.088 Btu/h-ft2-°F (R-9.4 ci) 

Roof –type Built up 

Roof R-value 0.053 Btu/h-ft2-°F (R-15 ci) 

Window U-factor 0.587 

Window SHGC* 0.39 

WWR** 30% 

Lighting System 

Lighting power density 1.0 w/ft2

Mechanical System 

Chiller type and COP Screw chiller, 5.0 COP 

Boiler eff 80% Ec (75% Et) 

SWH eff 80% Et 

 *SHGC = solar heat gain coefficient Ec = Combustion efficiency 

 **WWR = window to wall ratio Et = Thermal efficiency 
 8 

Development of Service Hot Water Load Estimates 

The service hot water load was calculated based on the estimated number of rooms in the hotel using the 

hotel data from Table 4, peak hot water consumption per person of 4 gallons per hour from ASHRAE 

(ASHRAE 1999). For sizing purposes, a 40° entering temperature was assumed. The delivery water 

temperature was assumed to be 140°F (The ASHRAE flow rates are assumed to be representative of the 

hot water delivered at the water heater delivery temperature). 

This results in a design hot water flow rate of 22.3 gpm per hotel wing, and a net hot water design load of 

1.11 million Btu/h. This is in excess of the 1,000,000 Btu/h that would trigger the heat recovery for 

service water heating code requirement. 

Default building use schedules, including hot water use schedules from DOE2.2 for the hotel were used in 

modeling the overall hot water load. Figure 1 shows the DOE2.2 hot water load schedule for a weekday. 

It should be noted that because the inlet water temperature to the heat recovery system varies during the 

year, the peak load for system design purposes may need to be typically higher in the winter than in the 

summer. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour of Day

Fraction of Design Hot Water Load

Figure 1. Hot Water Load Profile from DOE2.2, Hotel 
 9 

An estimate of the size for the water heating system was developed using the ASHRAE Applications 

Handbook information, looking at the tradeoff between storage and heat rate for the water heater system, 

as well as information provided on-line by A.O. Smith (2004), which suggests a minimum storage for 

300-350 hotel units of 700 gallons total. The final design implemented assumed 1,000 gallons of water 

storage, implemented using two 500-gallon commercial water heaters. The combined UA for this system, 

used for estimating standby loss, is approximately 88 Btu/h-°F based on ASHRAE 90.1-1999 service 

water heating. 
10 

Base Building Simulation

The hotel wing was simulated using the default building schedules from DOE2.2 as discussed previously, 

and using New York City typical meteorological year (TMY2) weather data. Figures 2 and 3, and Table 

6, show the month-by-month energy consumption for the building end-uses. The cooling and heat 

rejection equipment was sized to meet the peak capacity required for these systems during the annual 

simulation, with a 20% additional sizing allowance applied. As noted previously, the peak cooling 

capacity selected for this one wing, at 1.67 million Btu/h (729 ft2

/ton) was significantly lower than what 

would trigger the IECC2003 requirement. This may be partially caused by the significantly lower 

lighting levels assumed for hotel buildings in the IECC than those in previous building codes, as well as 

the result of the New York climate being somewhat cooler than that likely envisioned by the framers of 

the heat recovery requirement. Nevertheless, it was felt that doing the analysis on only one wing of the 

building would still provide a reasonable, if possibly conservative assessment of the economics for a 

simple heat recovery application. 

It must also be noted that for this simple building, the chiller load was only seen to be significant for 5 

months of the year. It is not clear how well this represents what might be thought of as “typical” loads for 

this size hotel building. However, because the IECC would require the use of water economizers to meet 

100% of cooling loads when outside air temperatures are less than 50°F dry bulb temperatures, 45°F wet 

bulb temperatures, chillers under these temperatures could effectively be scheduled off. The relatively 

fewer months of chiller operation compared to warmer climates would be expected to negatively impact 

the cost-effectiveness for a service hot water heat recovery system compared with a warmer climate. 

0

20

40

60

80

100

120

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Electrical Consumption (MWh)

Space Cool

Heat Reject.

Pumps & Aux.

Vent. Fans

Misc. Equip.

Area Lights

Figure 2. Electrical Energy Consumption for Base Hotel Building, by End Use. 
 11 

0

200

400

600

800

1000

1200

1400

1600

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Gas Consumption (million Btu)

Space Heat

Hot Water

Figure 3. Natural Gas Energy Consumption for Base Hotel Building, by End Use. 

Table 6 Energy Consumption for Base Hotel Building, by End Use. 

Electric 

Consumption 

(MWh) 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total 

Space Cool 0.0 0.0 0.2 0.5 6.9 21.9 33.5 29.1 18.9 1.6 0.0 0.0 112.5 

Heat Reject. 0.0 0.0 0.0 0.0 0.1 0.8 1.8 1.5 0.9 0.0 0.0 0.0 5.1 

Vent. Fans 6.9 6.2 6.9 6.7 6.9 6.7 6.9 6.9 6.7 6.9 6.7 6.9 81.4 

Pumps & Aux. 6.5 5.8 6.7 6.9 10.3 16.9 18.1 18.0 15.5 7.6 6.1 6.4 124.7 

Misc. Equip. 7.5 6.8 7.5 7.3 7.5 7.3 7.5 7.5 7.3 7.5 7.3 7.5 88.6 

Area Lights 28.8 26.0 28.8 27.9 28.8 27.9 28.8 28.8 27.9 28.8 27.9 28.8 339.2 

Total 49.7 44.9 50.1 49.3 60.5 81.5 96.7 91.8 77.2 52.4 47.9 49.7 751.6 

 

Gas 

Consumption 

(million Btu) 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total 

Space Heat 1006.6 783.8 642.7 369.7 74.2 0.0 0.0 0.0 7.6 171.7 493.9 789.0 4339.3 

Hot Water 344.3 323.2 358.0 339.9 324.0 288.3 274.9 261.0 252.1 273.0 285.6 320.9 3645.3 

Total 1350.9 1107.0 1000.7 709.7 398.1 288.3 274.9 261.0 259.8 444.8 779.6 1109.9 7984.6 
 12 

Condenser Heat Rejection and Service Hot Water Loads 

The following hourly data were extracted from the DOE2.2 base case simulation 

Chiller Plant Cooling Load 

Chiller Heat Rejection 

Chiller Electrical Power Consumed 

Chilled Supply Water Temperature 

Entering Condenser Water Temperature 

Service Hot Water Load 

Service Hot Water Make-up Water Temperature 

Service Hot Water Make-up Flow Rate 

Cooling Tower Heat Rejection Load 

Cooling Tower Fan Energy 

In addition, the hourly Leaving Condenser Water Temperature was calculated from the total heat rejection 

and the Entering Condenser Water Temperature, and loop flow rate. A constant flow rate was assumed 

for the chiller condenser during operation. 

Heat Recovery Strategy 

Several common strategies for heat recovery were examined from the outset of this task based on 

discussions with consulting engineers and a review of ASHRAE’s recently published Application Guide 

for Chiller Heat Recovery. (ASHRAE 1999b). The most common strategies were deemed to be 1) a 

separate condenser bundle on the screw chiller, but operating at typical heat rejection temperatures 

(<110°F) for a chiller; 2) a separate, smaller, heat recovery chiller servicing the main cooling loop and 

rejecting heat at a high temperature (Scroll chiller, 130°F heat rejection); and 3) a simple heat exchange 

process between the condenser water and the incoming make-up water. While both strategy (1) and (2) 

were deemed likely to result in high total energy savings, the relatively few hours of chiller operation per 

year suggested that a simpler strategy may be more cost effective and would satisfy the minimum 

requirement of the IECC to provide preheat of the peak hot water consumption to 85°F during peak 

cooling periods. 

A simple plate and frame heat exchanger, operating between the exiting condenser water temperature and 

the make-up supply water was assessed (see Figure 4). The heat exchanger was sized to provide a 5°F 

approach to the condenser water temperature at peak design hot water flow. Because the make-up service 

hot water flow is typically much less than the design flow during most of the year, a closer approach 

temperature would be achieved during most of the yearly operation. 
 13 

Plate Heat Exchanger

Condenser Return

Cooling Tower

Water Heater

SHW Loop Supply

SHW Makeup

SHW Loop Return

Chiller

Condenser

Figure 4. Schematic of Service Heat Recovery System 

A model of the heat exchange process using the NTU (number of transfer units) methodology was 

developed based on a preliminary sizing methodology for plate and frame heat exchangers outlined by 

Haslego (Haslego 2002). A spreadsheet implementation of this methodology was used to provide for 

approximate heat exchanger sizing, as well as generate first cost estimates as a function of the inlet 

conditions (temperatures and flow rates) and desired approach temperatures. 

A similar heat recovery model, based on the heat exchanger size (in NTU) from the above spreadsheet 

was implemented in a spreadsheet containing the hourly data output from the simulation. This allowed 

calculation of the total heat recovered by the heat exchanger when allowing for the hourly varying makeup water flow and available condenser heat and condenser outlet temperature. Separate calculations of 

additional pumping power for the SHW and condenser sides of the heat exchanger were also implemented 

in the hourly spreadsheet. 

 

At design conditions, the total heat rejected by the chiller is vastly greater than the peak hot water need. 

Some limited optimization was done to examine tradeoffs between maximum amount of heat recovery 

possible (achieved through larger heat exchangers and use of total condenser water flow rates) and simple 

systems that only used a fraction of the total condenser water (and a fraction of the available condenser 

heat) for the heat exchange process. This analysis suggested that utilizing approximately 25% of the 

condenser flow rate as input to the SHW heat exchanger provided a high ratio of the heat-recovery benefit 

to total pumping-cost on an annual basis (assuming a 15 psi pressure drop across the heat exchanger). 

The resulting sizing specifications of the heat exchange system are shown in Appendix A. The 

approximate cost of a stainless steel heat exchanger is also shown based on the cost estimating approach 

provided by Haslego. 

After the original analysis was used to determine an optimal condenser flow rate, a second, 

manufacturer’s heat exchanger sizing tool (Mueller 2004) was used to more formally size a heat 
 14 

exchanger with double wall vent. This second sizing, also shown in Appendix B, resulted in a heat 

exchanger with approximately three times the total plate area (70.5 ft2

 versus 23.6 ft2 from the Haslego 

method.). This is believed to be primarily a result of the lower rate of heat transfer caused by the double 

wall vented design. This second design did, however, result in lower total pressure drop through the heat 

exchanger (5.4 psig versus 15 psig specified in the original Haslego design). The final energy savings 

analysis was based on this second heat exchanger design. 

Hourly energy savings for the service hot water heat recovery system were calculated based on dividing 

the hourly heat recovered by the system by the assumed thermal efficiency for the water heater. 

Pumping costs were based on the design pressure drops using the manufacturer’s sizing tool. For this 

analysis, a constant thermal efficiency of 80% was assumed for the water heating system. 

Impact on Chiller Performance 

Because only standard condenser water temperatures were assumed for this analysis, no chiller efficiency 

degradation could be attributed to this heat recovery process. At very low chiller loads, there may be 

some performance gains because the entering condenser water temperature could be pre-cooled below the 

design entering temperature using the SHW make-up water. Additional savings for the simple heat 

exchanger strategy could be made through reduction of the condenser flow rate to increase the condenser 

leaving water temperature and the subsequent heat recovery. This would come at some reduction in the 

overall chiller performance, but would also reduce the load and energy consumption of the cooling tower 

(see below). 

Impacts to Heat Rejection Equipment 

Because the heat recovery removes heat from the chiller heat rejection loop, less heat rejection occurs at 

the cooling tower, reducing tower fan run time. In instances where large quantities of heat are removed 

(for instance, using a dedicated heat recovery chiller to meet 70% or more of summer hot water loads), 

this can be significant savings. To account for that effect in this study, the hourly tower fan energy was 

reduced by the same ratio as the condenser loads to the tower after accounting for heat recovery. For 

example, if 10% of the condenser load was used for heat recovery, the cooling tower fan energy was 

reduced by 10% for that hour. This assumes the towers use multiple cells and multiple fan speeds 

(required under IECC2003). 

Energy Cost Savings 

Annual energy cost savings for the heat recovery system were estimated at approximately $2400/yr based 

on monthly average New York State gas and electricity prices for 2003. (Energy Information 

Administration 2004). Table 7 shows expected monthly energy and energy cost savings for the heat 

recovery option examined. 
 15 

Table 7. Building Energy Impacts from Heat Recovery 

Gas 

(Million 

Btu) 

Electricity 

(1000 kWh) 

Month 

SHW Pump Tower 

Electricity

 (¢/kWh) 

Gas 

 

($/million 

Btu) 

Energy 

Cost 

Savings 

 ($) 

Jan 0.00 0.00 0.00 11.1 8.03 0 

Feb 0.00 0.00 0.00 11.8 8.53 0 

Mar (0.90) 0.01 (0.00) 12.6 10.01 8 

Apr (2.23) 0.03 (0.00) 13.1 9.70 18 

May (31.14) 0.18 (0.03) 13.0 9.48 275 

Jun (84.72) 0.36 (0.12) 13.6 9.15 742 

Jul (96.15) 0.38 (0.20) 14.4 8.27 770 

Aug (78.09) 0.38 (0.15) 14.5 7.80 577 

Sep (56.27) 0.33 (0.09) 14.3 7.91 412 

Oct (7.16) 0.07 (0.00) 13.8 7.99 47 

Nov 0.00 0.00 0.00 12.4 8.61 0 

Dec (0.03) 0.00 0.00 12.1 9.34 0 

Annual -356.70 1.74 -0.60 2849 

The estimated hot water energy savings for this system was approximately 10% of the hot water energy 

used in the base case building, or approximately 3.4% of the site energy use of the building. 

Installed Cost 

The first cost of the heat recovery system was estimated at $18,000 based on material and installation 

costs estimates shown in Appendix A. The material cost of the primary component, a plate and frame 

heat exchanger, was based on a quote from a manufacturer’s representative, attached in Appendix B. The 

balances of system costs were developed from Means (RS Means 2004). An average location factor 

increase of 113% was applied to the Means Cost estimates, based on the average of the New York 

location factors reported. 

Installation, piping and valves costs are largely unknown and would be specific to each individual 

installation. The costs provided here are approximate, based on the assumption that the domestic water 

feed line and the chiller condenser flow loop have been designed to be within relatively close proximity at 

some point in the building. Allowances for 40 ft of piping on either side of the heat exchanger have been 

provided. 

Estimated Payback 

Based on the annual energy savings of $2850 and the $18,000 installed cost of the service hot water heat 

recovery system, the simple payback for the system was 6.3 yrs. This is under the 10-year payback 

threshold established for the state of New York. 
16 

Conclusion 

The analysis presented suggested that the simple condenser heat exchanger could provide a cost-effective 

way to meet the IECC2003’s heat recovery for service water heating requirement in a typical hotel 

application. It is expected that it would also be cost-effective in inpatient hospital applications, one of the 

other likely building types to which this requirement would apply. It would also be expected to be costeffective in multifamily residential buildings, where central water-cooled cooling might be used. 

The analysis of buildings also suggested that there may be other building types, such as very large offices, 

which may meet the criteria under the IECC, but whose load profiles for hot water use may be very 

different than that of the more common hotel/motel. No actual analysis was done to examine the costeffectiveness for these buildings. 

It is recognized that other heat recovery strategies may be more cost-effective and may result in greater 

savings in this or in similar applications, and this report should not be interpreted as recommending one 

heat recovery strategy over another. 
17 

References 

A.O. Smith. 2004. Hot Water Requirements - Motels and Hotels. 

http://www.hotwater.com/PDFSpecSheets/B105.pdf, accessed June 2004 

ASHRAE. 1999. ASHRAE Applications Handbook, American Society of Heating, Refrigerating, and Air 

Conditioning Engineers, Atlanta, Georgia. 

ASHRAE . 1999b. Application Guide for Chiller Heat Recovery. American Society of Heating, 

Refrigerating, and Air Conditioning Engineers, Atlanta, Georgia. 

ASHRAE 90.1. 1999. 

ASHRAE 90.1. 2001. 

Bell. 2000. HVAC Equations, Data, and Rules of Thumb. McGraw Hill, New York. 

DOE. 2000. Screening Analysis for EPACT Covered Commercial HVAC and Water Heating 

Equipment. U.S. Department of Energy, Washington, D.C. 

Energy information Administration (EIA). 1997. 1995 Commercial Building Energy Consumption 

Survey. U.S. Department of Energy Energy Information Administration, Washington, D.C. 

http://www.eia.doe.gov/emeu/cbecs/

Energy Information Administration (EIA). 2004. Electric Power Monthly, June 2004, EIA website: 

http://tonto.eia.doe.gov/FTPROOT/electricity/epm/02260406.pdf, U.S. Department of Energy. 

Washington D.C. 

Haslego. 2002. Designing Plate-and-Frame Heat Exchangers. CEP Magazine, September. 

Hirsch. 2003. DOE2.2 Building Energy Use and Cost Analysis Program. (http://www.doe2.com/) 

George. 2003 Sizing water heaters for hotels and motels. PMEngineer, Vol 3. Viewable online at 

http://www.pmengineer.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2732,93793,00.h

tml accessed May 2004 

IECC. 2003. International Energy Conservation Code, International Code Council, Inc. Country Club 

Hills, Ilinois. 

Meyer. 2001. Hot Water for the Road. Energy Systems. October. 

http://www.esmagazine.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2503,66234,00.h

tml, accessed May 2004 

Mueller. 2004. Online Accu-Therm Plate and Frame Heat Exchanger Sizing Tool and Engineering 

Support. (http://www.muel.com/products/heattransfer/plate/, accessed August 2004) 
 18 

R.S. Means. 2004. Mechanical Cost Data, 27th Annual Edition. RS Means, Kingston, Massachusetts. 
Appendix A 

Design Parameters for Plate Heat Exchanger 
 20 

Appendix A Design Parameters for Plate Heat Exchanger 

Table A-1 Design Parameters for Plate Heat Exchanger System (Haslego) 

Service Hot Water Side 

 Entering water temperature at design (F) 60 

 Maximum design SHW water flow (gpm) 22.3 

 Approach (F) 5 

 Acceptable SHW pressure drop at design (psid) 15 

 Heat capacity (Btu/F) 11125 

Condenser Side 

 Condenser water inlet temp at design (F) 95 

 Condenser water flow (gpm) 96.2 

 Heat capacity (Btu/F) 47920 

 Acceptable condenser pressure drop at design (psid) 

Design 

 Cmin/Cmax at design 0.23 

 Leaving SHW temp at design 90 

 Leaving condenser water temp 88.0 

 Total heat transferred 333760 

 Eff 0.86 

 Log mean temperature differential 13.36 

 NTU_condenser 0.52 

 NTU_shw 2.25 

 h_condenser, 15 psi (Btu/hr-ft2-°F) 2800 

 h_shw, 15 psi (Btu/hr°t2-°F) 2500 

 

Plate type 

Type 316 

Stainless, 

0.5 mm 

 U (Btu/h-ft2-°F) 1057 

Q = UA LMTD 

 Area (ft2) 23.63 

 UA (Btu/h-°F) 24980 

Cost 

 Cost ($) 1881 
 21 

Table A-2 Final Double Wall-Vented Plate Heat Exchanger Specification Sheet used in Energy Savings 
Appendix B 

Estimated Costs for Heat Recovery System 
23 

Appendix B Estimated Costs for Heat Recovery System 

Table B-1 Material, Labor, and Total Estimated Installation Cost for Heat Recovery System 

Material Qty Material Cost 

 ($) 

Labor 

($) 

Total 

($) 

Total with 

Overhead & 

Profit 

($) 

Plate and frame heat 

exchanger UA= 358 Btu/ft2

-

h-°F 

1 7,500 215 7,715 9644

Pipe, black steel, 2-in. dia, 40 

ft with couplings and hangers 

1 145.6 356 501.6 696

2-in. iron elbows 4 34 126 160 228

6-in. pipe T, reducing 2 840 444 1284 1590

2-in. gate valve, bronze 4 332 116 448 536

2-in. balancing valve, bronze 1 355 40 395 450

2-in. strainers, Y-type 2 55 80 135 179

Pipe, copper, 2-in. dia, 40 ft, 

type L 

1 182 302 484 652

2-in. copper elbows 4 28.4 116 144.4 204

Condenser loop pump, 2 hp 1 1250 248 1498 1750

Total 10,722 2,043 12,765 15,929

Total with Average New York Location Factor Markup (113%) 17,999