COMBINED HEAT AND POWER

IN MULTIFAMILY HOUSING

USER MANUAL

for

HUD CHP Feasibility Screening Tool Version 2.1

April 30 Draft, 2008

Manual developed by

U.S. Department of Energy, Oak Ridge National Laboratory

for

U.S. Department of Housing and Urban Development

# Table of Contents

[Table of Contents 2](#table-of-contents)

[Getting Started 4](#getting-started)

[What is the HUD CHP Feasibility Screening Tool and who should use it?
4](#what-is-the-hud-chp-feasibility-screening-tool-and-who-should-use-it)

[What does the HUD CHP Tool do? 4](#what-does-the-hud-chp-tool-do)

[How do I use the HUD CHP Tool? 4](#how-do-i-use-the-hud-chp-tool)

[Overview of the HUD CHP Tool 5](#overview-of-the-hud-chp-tool)

[Data Forms & Results 5](#data-forms-results)

[Monthly Utility Data 5](#monthly-utility-data)

[Utility Rate Data 6](#utility-rate-data)

[Miscellaneous Input Information 7](#miscellaneous-input-information)

[Energy Plots 8](#energy-plots)

[Results 10](#results)

[Menu Commands 12](#menu-commands)

[File Menu 12](#file-menu)

[Print Options Form under File Menu
14](#print-options-form-under-file-menu)

[Print: Side-By-Side Comparison of Results
16](#print-side-by-side-comparison-of-results)

[Print: Method 1 Intermediate Results
16](#print-method-1-intermediate-results)

[Print: Method 2 Intermediate Results
17](#print-method-2-intermediate-results)

[Print: Method 3 Intermediate Results
18](#print-method-3-intermediate-results)

[Data Menu 20](#data-menu)

[Help Item 20](#help-item)

[Electric Generation and Prime Movers
20](#electric-generation-and-prime-movers)

[Reciprocating Engine Generators 21](#reciprocating-engine-generators)

[Equipment Cost 21](#equipment-cost)

[Installation Cost 21](#installation-cost)

[Heat Rate and Efficiency 22](#heat-rate-and-efficiency)

[Heat Recovery 22](#heat-recovery)

[Operating and Maintenance Costs 23](#operating-and-maintenance-costs)

[Gas Turbine Generators 23](#gas-turbine-generators)

[Equipment Cost 23](#equipment-cost-1)

[Installation Cost 23](#installation-cost-1)

[Heat Rate and Efficiency 24](#heat-rate-and-efficiency-1)

[Heat Recovery 24](#heat-recovery-1)

[Operating and Maintenance Costs 25](#operating-and-maintenance-costs-1)

[Microturbine Generators 25](#microturbine-generators)

[Equipment Cost 25](#equipment-cost-2)

[Installation Cost 26](#installation-cost-2)

[Heat Rate and Efficiency 26](#heat-rate-and-efficiency-2)

[Heat Recovery 26](#heat-recovery-2)

[Operating and Maintenance Costs 27](#operating-and-maintenance-costs-2)

[Algorithms and Methodology 27](#algorithms-and-methodology)

["Method 1" Algorithms 27](#method-1-algorithms)

["Method 2" Algorithms 29](#method-2-algorithms)

[Method 2 Assumptions & Methodology:
29](#method-2-assumptions-methodology)

[Method 2 Results 30](#method-2-results)

["Method 3" Algorithms 33](#method-3-algorithms)

[Details of Method 3 Calculations using the Sample Data:
36](#details-of-method-3-calculations-using-the-sample-data)

[Method 3 Assumptions & Methodology Applied to the Sample Data
38](#method-3-assumptions-methodology-applied-to-the-sample-data)

[Additional Information on Building Loads
38](#additional-information-on-building-loads)

[Electrical & Thermal Loads 38](#electrical-thermal-loads)

[Electrical Loads 39](#electrical-loads)

[Space Heating & Hot Water Loads 40](#space-heating-hot-water-loads)

[Map of EIA Climate Zones for 2001 Residential Energy Consumption Survey
(RECS) 40](#map-of-eia-climate-zones-for-2001-recs)

# Getting Started

## What is the HUD CHP Feasibility Screening Tool and who should use it?

Combined heat and power (CHP) (or cogeneration) is the production of
electricity and use of the heat created in that process. Putting heat
recovery together with power generation can provide essentially free
energy in the form of hot water or steam. In residential applications
the heat can be used for domestic hot water, space heating, absorption
cooling, or dehumidifying, at the building where it is produced. CHP
systems consist of a package of equipment with a prime mover (for
apartment buildings, most often a reciprocating engine or microturbine)
driving an electric generator. If all of the recoverable heat is used,
they can achieve overall efficiencies of about 80%, in contrast to the
33% average of more typical systems where electricity is produced at
central power plants. CHP avoids transmission losses and reduces
environmental impact.

The economic evaluation of proposed installations of combined cooling,
heating, and power systems in multi-family housing units requires
calculations that consider building heating, cooling, hot water, and
electrical loads, the costs of power and natural gas, and the simulated
performance of generators, chillers, boilers, and water heaters.
Sometimes it is possible to simplify this process to get a "go/no-go"
answer as to whether or not a building owner or operator should look
more carefully into CHP and perhaps enlist some engineering support in
conducting a site inspection and a rigorous economic analysis. The HUD
CHP Feasibility Screening Tool is one of several tools available for
"screening level" CHP analysis; this tool is "non-technical" and is
directed specifically toward building owners and operators. The tool may
be installed from the following website:

<http://eber.ed.ornl.gov/HUD_CHP_Guide_version_2.1/>

While CHP is not recommended for emergency generators, it is frequently
attractive in baseload or peak shaving operation with reciprocating
engine driven generators, gas turbine generators, microturbines, or fuel
cells. All-electric buildings are good prospects for installing CHP, but
this Tool will not analyze them. The better prospects for installing CHP
are single apartment buildings with 100 or more units, master metered
for electricity, with a central domestic hot water system, and with
access to gas.

## What does the HUD CHP Tool do?

The HUD CHP Tool performs a coarse economic assessment of the viability
of installing on site power generation combined with recovery of
generator heat for use in producing domestic hot water, space heating,
or even air conditioning using a heat driven absorption chiller. It does
this assessment by using information provided by the user, primarily
from the electric and gas utility bills, and some built in correlations
for generator performance and costs. The energy cost and consumption
data and generator information are combined to provide an estimate of
the simple payback from installing combined cooling, heating, and power
(CHP) at the site.

## How do I use the HUD CHP Tool?

The first step is to collect old billing information for both power and
heating. The electric energy use or consumption and monthly peak demand
and cost information can be found on the electric bills for the prior
twelve months. Heating bill information can be from fuel oil purchases,
natural gas, or steam purchased from a district energy system. Data are
needed for a primary fuel and as an option information can also be
provided for a secondary fuel.

The user also needs to be prepared to provide information about the
electric and natural gas utility tariffs. This includes:

-   the electric consumption or use charge (\$/kWh),

-   any fuel adjustment charge used by the utility (\$/kWh),

-   the peak demand rate (\$/kW),

-   any electric utility standby charges for providing backup capacity
    whenever the on site generator is down for scheduled or unscheduled
    maintenance, and

-   the cost of natural gas.

The user enters these numbers into a "fill in the blank" form and an
estimated simple payback is returned.

# Overview of the HUD CHP Tool

The HUD CHP Tool can be used to do a preliminary screening of the
economic potential of combined heating and power or combined cooling,
heating, and power in specific multifamily housing and apartment
buildings. The Tool uses information the user provides about the
building and energy costs from utility bills to make coarse estimates of
the hot water and space heating and cooling loads. These estimates are
combined with built-in data for electric generators to calculate
approximate energy and cost savings from operating on site generators
with heat recovery for domestic hot water, space heating, and space
cooling. The estimated system installed cost is divided by annual
savings on energy costs to calculate a simple payback in years.

# Data Forms & Results

The CHP Tool consists of a data form with several data "tabs." These
include the principal data entry forms under "Monthly Utility Data,"
"Utility Rate Data," supplementary information under "Misc. Input
Information," and calculated savings and payback under "Results."

## Monthly Utility Data

For the first form, the principal input data consist of information from
the user's monthly utility bills (Figure 1). There are three columns of
numbers from the electric bills and two sets of two columns each for
fuel consumption. Many sites will only use a single source of fuel for
boilers, water heaters, or furnaces and they will only need to fill in
the columns for "Fuel #1." Sites that use two fossil fuels, for example
natural gas and #2 fuel oil, complete both sets of columns for fuel
data. Users need to select a type of fuel or energy for the pair(s) of
column used and also the units of consumption in the case of natural gas
(i.e. therms, decatherms, million Btu's, hundreds of standard cubic
feet, or thousands of standard cubic feet). Fuel oil data are assumed to
be in gallons and purchased steam in thousands of pounds.

The table of numbers should be completed as carefully as possible using
data from monthly utility bills. The user does not need to include ","
or "\$" in the numbers as they are typed; the Tool will format each
number as it proceeds. Use either the "Tab" or "Enter" keys to move from
one data entry point to the next. Use Shift+Tab to move backwards. The
average cost of power for the year is computed below the third column
from the left for informational purposes (a bit of a reality check for
misplaced decimal points) and below the Fuels columns. (Note that if
monthly data are not available, Method 3 can still produce results from
utility rate data entered on the second tab.)

![](media/image1.wmf){width="5.9875in" height="4.240277777777778in"}

Figure 1 --- Monthly utility data entry form.

## Utility Rate Data

The second form (second tab, Figure 2) contains two blocks of
information about the utility rate structures. Many electric utilities
use multiple block tariff structures, so the user should enter energy
and demand rates "at the margin" \-- the highest block where they are
actually purchasing power since this is what would have applied to power
generated on site. Many utilities use a basic energy charge (\$/kWh) and
also a fuel adjustment charge (\$/kWh) to recoup their own costs as fuel
prices increase. Savings from avoidance of purchased utility power are
calculated using the sum of the energy charge and the fuel adjustment
charge. The Tool assumes that any on-site power generation is produced
using a natural gas-fired generator and it provides for the cost of gas
to be computed using a flat rate. The "option" buttons are used to
select the units of natural gas consumption.

![](media/image2.wmf){width="5.670138888888889in"
height="1.8194444444444444in"}

Figure 2 --- Utility rate data form.

## Miscellaneous Input Information

![](media/image3.jpeg){width="5.3799212598425195in"
height="3.6854330708661416in"}CHP calculations are performed using three
different methods of estimating the building thermal loads. One of these
methods employs a table of information for heating and cooling degree
days that has been built into the Tool. In the third tab (Figure 3)
users can select a state from the list under item "1" on this tab and
then a city within that state from item "2." The corresponding heating
and cooling degree days selection for a typical year are based on this
location. These are correlated to "energy intensity factors" (see Method
3 Algorithms) to estimate space heating and cooling loads using items 3a
and b on this tab. The "Prime Mover" box at the bottom has different
technology types "greyed out" depending on the size of system needed. If
microturbines are an appropriate choice for the building, they will be
available as a prime mover, but the sample building load is over 400 kW
(Figure 4), so microturbines are not allowed as a reasonable screening
choice for this building (a later more detailed analysis could include
them).

Domestic hot water loads are estimated using an average per capita daily
hot water usage and annual average ground temperature (cold water
entering the water heater tank) for the city specified in item "2." The
approximate number of residents in the building is specified in Item 4
and a subjective measure of relative hot water consumption is chosen in
Item 5. Hot water loads are estimated using these selections with data
for multifamily housing hot water consumption reported by Goldner (1994,
see "Method 3 Algorithms" for citation).

Methods 1 and 3 size the generator using the highest monthly power
consumption (kWh) and an assumed generator "run time fraction." The
built-in sample data set, for instance, is for a site that uses 56,400
to 138,000 kWh per month with the maximum of 138,000 kWh occurring in
August. This amount of power would be produced by a 247 kW generator
(138,000 kWh / \[31 days x 24 hr/day x 0.75\] ). A 250 kW generator
would be the closest commercially available capacity to the computed
size. A default run time fraction of 0.75 is built into the HUD CHP
Tool, but this value can be changed by the user by selecting a number in
Item 6 on the "Misc. Input Information" tab.

Fuel consumption data on the "Monthly Utility Data" tab are converted to
heat and hot water loads using an assumed furnace, boiler, or water
heater efficiency. There is a place on the "Misc. Input Information" tab
where the user can change the built-in value for annual heating
efficiency to another value using Item 7 if desired.

The "Misc. Input Information" tab is used so the user can change some
default parameters used in the calculations. The CHP economic results
are computed three different ways using different methods to estimate
the heating and cooling loads. Each of the methods use data built into
the Tool for generator equipment cost, installation cost, maintenance
cost, and operating efficiency. The user selects information by
specifying the type of generator to be used (i.e. reciprocating-engine,
gas turbine, microturbine, or fuel cell) using the buttons at the bottom
of this page. Reciprocating-engines, microturbines, and fuel cells are
available (or soon will be) across the entire range of generator
capacities applicable to multifamily housing, so these choices are
always available. Gas turbines, however, are only applicable to the
largest installations and this choice is only available if the estimated
capacity is greater than 1,000 kW.

## Energy Plots

The "Energy Plots" tab of the main data form contains two rows of bar
charts. The three charts at the top half of the page display the user
supplied information (Input Data) from the "Monthly Utility Data" tab
and shows (a) electric power consumption in kWh, (b) electric demand in
kW, and (c) total fossil fuel consumption for heating and hot water in
millions of Btu's (MMBtu). These charts should show distinct differences
in energy use between the summer and winter months. If power and fuel
consumption are fairly level throughout the year (i.e. bars all about
the same height), then "Method 1" and "Method 2" may not give good
estimates of heating and cooling loads that are subsequently used in the
CHP calculations.

The three charts at the bottom of this page display results for the CHP
simulation using "Method 2." The blue bars in the chart on the left show
the amount of electricity generated by the CHP system each month and the
red bars the amount of electricity supplied by the utility. By comparing
red bars in the upper chart for electricity purchased for the baseline
system with the red bars in the lower chart for the CHP system, the user
can see reductions in purchased utility power due to CHP. Likewise, the
center chart at the bottom shows the maximum monthly power demand for
the CHP system with the purchased utility demand in red and the CHP
system capacity in blue. CHP systems that use recovered heat in
absorption chillers to provide air conditioning will also have a green
bar that indicates avoided power demand by using absorption air
conditioning. Once again, the red bars in the upper and lower charts can
be compared to see reductions in utility demand due to the CHP system.

![](media/image4.wmf){width="6.4944444444444445in"
height="5.277777777777778in"}

Figure 3 --- Energy plots.

The lower chart on the far right displays data for the monthly fuel
consumption. The red segments correspond to boiler and water heater fuel
and the blue segments correspond to fuel use for the CHP generator.

## Results

The HUD CHP Tool performs three separate sets of calculations that are
summarized on the "Results" tab. This brief summary provides the range
of simple payback periods from the analyses and also the range in
generator capacities assumed. There is also a group of "check boxes"
that can be used to display additional information about the
calculations. Information about the assumptions and algorithms used in
the calculations can be displayed by clicking the check box for
"Summary."

![](media/image5.wmf){width="5.9875in" height="1.9951388888888888in"}

Figure 4 --- Results tab.

The first method used for the calculations is for a CHP system that only
uses recovered heat for domestic hot water; no recovered heat is
assigned for space heating or powering an absorption chiller for space
cooling. Hot water consumption is estimated from the utility data
specified for the summer months (May through September) on the "Monthly
Utility Data" tab. Electricity and natural gas costs are also taken from
the input data for the gas and electric utilities on that data tab (at
the bottom of the page, not the table of monthly usage and cost).

The second method assumes a CHP system that uses recovered heat for
(1)domestic hot water, (2)space heating, and (3)space cooling with an
absorption chiller. This algorithm also derives hot water and heating
and cooling loads from the table of monthly fuel and power consumption
and uses the input utility data for power consumption, demand rates,
natural gas costs, etc. from the "Energy & Utility Data" tab. This
algorithm performs a month-by-month evaluation and selects the generator
size that provides the shortest simple payback.

The third method estimates annual heating and cooling loads from the
building location and algorithms published by the Department of Energy's
Energy Information Administration based on heating and cooling degree
days. It also uses the electric and gas utility rate information to
calculate system operating costs.

Whether or not a CHP would be economical depends on the type and size of
generator installed, the equipment and installation costs, generator
efficiency, heat recovery rate, and annual maintenance costs. All of the
generator related parameters vary by equipment type (i.e.
reciprocating-engine, gas turbine, microturbine, fuel cell). CHP system
installation costs can vary widely depending on site specific conditions
(e.g. location and capacity of transformers, relocation of existing
equipment, distance from gas line, gas line pressure). The user can use
the buttons located on tab "Misc. Input Information" to select the type
of generator and difficulty of installation. Simple payback is computed
as the sum of the equipment and installation cost divided by the
difference between the baseline operating cost (i.e. utility power and
boiler/water heater fuel) and the CHP operating cost (generator and
boiler/water heater fuel, generator maintenance costs, and any necessary
utility power).

![](media/image6.wmf){width="5.9875in" height="5.040277777777778in"}

Figure 5 --- Summary notes displayed when "Summary" check box is
checked.

# Menu Commands

![](media/image7.jpeg){width="4.103543307086614in" height="1.0in"}The
HUD CHP Tool data form includes a menu bar to assist in data entry,
printing, and maneuvering throughout the form. It is located at the
upper-left of the form, as shown in Figure 7.

## File Menu

![](media/image8.jpeg){width="4.25in" height="2.4480314960629923in"}The
File Menu can be used to start a new data file, print a summary of the
current set of calculations, open and save data files, and exit the
Tool. These commands can be invoked by clicking them with the mouse
cursor, using the "Alt" key on the computer, or with the "CONTROL" key.
Pressing "Alt" by itself causes the entries on the menu bar to be
displayed with the "F" "D" and "H" underlined. Holding down "Alt" and
pressing "F" displays the file menu. Continuing to hold the "Alt" key
down and pressing another letter invokes one of the menu options:

-   "N" clears all of the data selections for a new set of information,

-   "P" prints the current set of information,

-   "O" initiates the process of opening an existing data set,

-   "S" saves the current set of data,

-   "A" initiates the process of saving the present data under a new
    name, and

-   "X" exits the Tool.

The file commands can also be invoked by holding down the control key,
"Ctrl," while typing "N" "P" "O" "S" "A" or "X".

The last item on the "File Menu," "Capture Screen Shots," is a new
feature. It allows the user to automatically create a Microsoft Word
file that contains images of the HUD CHP Tool data tabs that are "open."
Remember that additional tabs can be "opened" by clicking on the option
boxes for "Summary," "Method 1," "Method 2," or "Method 3" on the
"Results" tab. The screen captures put into the Word file are of all
open tabs, so there can be differences depending on which tabs are open
at the time. The tab screens captured by default are:

-   Monthly Utility Data

-   Utility Rate Data

-   Miscellaneous Input Information

-   Energy Plots

-   Summary of Results

-   Comparison of Methods

This command can be invoked by using the menu directly or by pressing
"Ctrl" and "H" keys together. The screen shots are stored in The HUD CHP
Tool opens a Word document named "ScreenShots.DOC" in the currently
active folder or subdirectory and places each screen shot into separate
paragraphs. Word is left open, but it is "minimized" to an icon on the
Windows Taskbar (Figure 9):

![](media/image9.jpeg){width="5.997222222222222in"
height="2.397222222222222in"}

Figure 6 --- Windows Taskbar showing ScreenShots.doc task item.

Clicking on the mouse on the Word task item on the Windows Taskbar
(circled in red above) restores the Word window to the computer display
(Figure 10). The screen images in the Word file can be copied into other
Windows applications using the "Cut" and "Paste" commands or left in the
Word file (it is recommended that the user use the "File, Save As"
commands in Word to save the file with a new file name since
"ScreenShots.doc" will be reused by the HUD CHP Tool each time the
"Capture Screen Shot" command is invoked and any old data will be
overwritten).

![](media/image10.jpeg){width="5.997916666666667in"
height="6.954861111111111in"}

Figure 7 --- ScreenShots.doc Word window restored to working size with
first captured screen shots.

## Print Options Form under File Menu

There are five options for printing that are selected from a form, as
shown in Figure 11. They enable the user to limit the printing to the
input data and summary results or to choose the details of the three
Methods. They are illustrated using the Sample Data, a composite created
from several sources. A printout of the sample input data and Summary of
Results from those data are shown next.

HUD CHP Feasibility Screening Tool

\<\< Sample Data \>\>

Electricity

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- #2 fuel oil Fuel #2

Power Demand \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

Month kWh kW Cost gallons Cost therms cost

January 68,400 138 \$8,058 27,979 \$68,548

February 67,800 132 \$7,980 25,326 \$62,053

March 57,000 132 \$6,709 29,645 \$72,630

April 56,400 126 \$6,638 16,939 \$41,500

May 57,600 150 \$6,674 7,390 \$18,105

June 117,600 400 \$13,842 6,797 \$16,992

July 138,000 432 \$16,242 5,532 \$13,553

August 136,800 402 \$16,101 4,722 \$11,569

September 90,600 276 \$10,663 6,405 \$15,692

October 61,200 174 \$7,203 12,761 \$31,264

November 63,600 138 \$7,486 15,407 \$37,747

December 69,000 138 \$8,121 24,922 \$61,059

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

Annual Total 984,000 \$115,717 183,827 \$450,712

Average Cost \$0.118 \$2.452

Electric Utility Rate Data

Energy Charge \$0.0444/kWh Natural Gas Utility Rate Data

Fuel Adjustment Charge \$0.0733/kWh cost of gas \$1.3119/CCF

Demand Charge \$0.00/kW/month

Standby Charge \$0.00/kW/month

Location: Philadelphia, Pennsylvania

Building Specifications: Equipment Specifications:

heated floor space 98,000 sq ft recip-engine driven generator

air conditioned floor space 98,000 sq ft typical installation costs

approx. number of occupants 200 low hot water usage

Results:

1\. Recovered Heat for Domestic Hot Water Only (Loads Estimated from
Utility Bills)

a\. simple payback of 5.4 years

b\. potable hot water load estimated from summer fuel consumption

c\. generator sized to meet potable hot wate4r loads operating 7,440
hours/year

d\. 107 kW recip-engine generator

2\. Recovered Heat for Heating, Air Conditioning and

Domestic Hot Water (Loads Estimated from Utility Bills)

a\. simple payback of 6.0 years

b\. space heating, cooling, and potable hot water loads estimated

from monthly power and fuel consumption

c\. generator sized to meet heating, cooling, and hot water loads
operating

6,570 hours/year

d\. 110 kW recip-engine generator

3\. Recovered Heat Used for Heating, Air Conditioning, and Domestic Hot
Water

(Space Conditioning Loads Estimated from EIA Degree-Day Algorithms and

Hot Water Use Estimated from ASHRAE Publications)

a\. simple payback of 8.3 years

b\. space heating and cooling estimated using heating and cooling degree
days

for Philadelphia, Pennsylvania using EIA algorithms

c\. potable hot water load estimated using high hot water usage for
multifamily

ground and hot water tank temperatures of 54.1 F and 140.0 F

d\. generator sized to meet heating, cooling, and potable hot water
loads

operating 6,570 hours/year

e\. 51 kW recip-engine generator

### ![](media/image11.jpeg){width="4.0in" height="2.3866141732283466in"}Print: Side-By-Side Comparison of Results

Selecting the "Side-By-Side Comparison of Results for all Three Methods"
option on the "Print Options" form, as shown in Figure 11 causes the
results below to be sent to the computer default printer when the Print
button is clicked.

HUD CHP Feasibility Screening Tool

Sample Data

Comparison of Loads and CHP System Information for Alternative
Calculational Procedures:

Method 1 Method 2 Method 3

1\. Service Hot Water Load 7,607 7,607 1,874 MMBtu

2\. Space Heating & Hot Water Load 11,281 2,385 MMBtu

3\. Space Cooling Load 2,756 1,909 MMBtu

4\. Total Thermal Load 7,607 21,643 6,618 MMBtu

5\. Generator Capacity 107 110 51 kW

6\. Operating Time 7,440 6,570 6,570 hours

7\. Power Output 799,014 729,000 331,790 kWh

8\. Recovered Heat 4,451 4,040 2,068 MMBtu

9\. Installed Cost \$200,992 \$203,718 \$141,471

10\. Annual Operating Savings \$37,377 \$34,001 \$16,963

11\. Simple Payback 5.4 6.0 8.3 years

### Print: Method 1 Intermediate Results

Selecting the "Method 1 Intermediate Results" option on the "Print
Options" form (refer to Figure 11) causes the results shown below to be
sent to the computer default printer.

HUD CHP Feasibility Screening Tool

\<\< Sample Data \>\>

Details of Method 1 Calculations:

1\. Cogeneration System Description

a\. generator capacity 107 kW

b\. generator heat rate (29.7% LHV) 11,474 Btu/kWh

c\. generator heat recovery rate 5,571 Btu/kWh

d\. annual operating time 7,440 hrs

Baseline 107 kW

2\. Power Consumption System Recip-Engine CHP

a\. utility power 984,000 184,986 kWh

b\. on-site generation 0 799,014 kWh

c\. total power consumed 984,000 984,000 kWh

d\. approx. cost

\(1\) energy & fuel adj chg \$115,817 \$21,773

\(2\) demand & standby charges \$0 \$0

\(3\) total approx. cost \$115,817 \$21,773

3\. Water Heater Summary

a\. hot water load 7,607 7,607 MMBtu

b\. recovered heat 0 -4,451 MMBtu

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\--

c\. net water heater output 7,607 3,155 MMBtu

d\. estimated fuel consumption 10,142 4,207 MMBtu

4\. Fuel Consumption

a\. water heater 10,142 4,207 MMBtu

b\. generator 0 9,168 MMBtu

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\--

c\. total fuel consumption 10,142 13,375 MMBtu

d\. approx. cost \$136,646 \$180,199

5\. Annual Operating Cost

a\. purchased electricity \$115,817 \$21,773

b\. natural gas \$136,646 \$180,199

c\. gen-set O&M \$0 \$13,113

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\--

d\. total operating cost \$252,462 \$215,085

e\. annual operating savings (loss) \$37,377

6\. Simple Payback

a\. estimated gen-set installed cost \$200,992

b\. annual operating savings (loss) \$37,377

c\. simple payback 5.4 yrs

Method 1 Assumptions & Methodology

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

1\. Hot Water Heater Uses Fossil Fuel(s)

a\. cost of fuel #1 and fuel #2 used to estimate annual cost of heating
water

b\. fuel consumption figures used only to calculate average cost of fuel
as

a quick visual check of the data

2\. Electrical Power Consumption and Monthly Peak Demand Data

a\. used in sizing generator, efficiency, and heat recovery

b\. monthly cost data only used to compute average cost of power as a
quick visual check

3\. Electric and Natural Gas Utility Data

a\. used to estimate cost of operating generator

b\. used to estimate avoided cost of purchased cost of electricity

### Print: Method 2 Intermediate Results

HUD CHP Feasibility Screening Tool

\<\< Sample Data \>\>

Details of Method 2 Calculations (priority use of recovered heat to
heating):

Generator Parameters: Simple Payback:

capacity 110 kW baseline operating cost \$455,125

equipment cost \$1,294/kW CHP operating cost \$421,124

installation cost \$558/kW annual operating savings/losses \$34,001

total installed cost \$1,852/kW CHP system capital cost \$203,718

simple payback 5.99 years

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

Minimum Simple Payback Occurs for:

a\. generator capacity 110 kW

b\. heat & hot water load 485 MMBtu

c\. space cooling load 881 MMBtu

Gen-Set Total Total Total Total Total Total Total Simple

Capacity Cost Cost Cost Cost Cost Cost Annual Payback

kW Jan-Feb Mar-Apr May-Jun Jul-Aug Sep-Oct Nov-Dec Cost years

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

0 \$114,425 \$99,332 \$46,807 \$51,271 \$53,244 \$90,046 \$455,125 999.0

12 \$113,607 \$98,514 \$45,990 \$50,453 \$52,426 \$89,229 \$450,219 20.7

25 \$112,926 \$97,833 \$45,308 \$49,772 \$51,744 \$88,547 \$446,129 12.7

37 \$112,278 \$97,185 \$44,660 \$49,124 \$51,096 \$87,899 \$442,243 9.9

49 \$111,649 \$96,556 \$44,031 \$48,494 \$50,467 \$87,270 \$438,467 8.4

62 \$111,031 \$95,939 \$43,414 \$47,877 \$49,850 \$86,653 \$434,764 7.5

74 \$110,423 \$95,330 \$42,805 \$47,269 \$49,242 \$86,044 \$431,113 6.9

87 \$109,821 \$94,728 \$42,204 \$46,667 \$48,640 \$85,443 \$427,502 6.5

99 \$109,225 \$94,132 \$41,607 \$46,070 \$48,043 \$84,846 \$423,923 6.2

111 \$108,632 \$94,043 \$41,225 \$45,478 \$47,493 \$84,254 \$421,124 6.0

124 \$108,127 \$94,088 \$40,953 \$44,889 \$47,223 \$83,915 \$419,194 6.1

136 \$108,174 \$94,127 \$40,680 \$44,303 \$46,951 \$83,960 \$418,195 6.3

148 \$108,215 \$94,161 \$40,406 \$43,720 \$46,678 \$84,000 \$417,180 6.4

161 \$108,251 \$94,192 \$40,131 \$43,139 \$46,403 \$84,036 \$416,152 6.6

173 \$108,284 \$94,219 \$39,855 \$42,847 \$46,399 \$84,068 \$415,671 6.8

185 \$108,313 \$94,243 \$39,578 \$42,814 \$46,432 \$84,096 \$415,477 7.1

198 \$108,340 \$94,266 \$39,302 \$42,777 \$46,461 \$84,122 \$415,267 7.4

210 \$108,364 \$94,286 \$39,024 \$43,146 \$46,488 \$84,146 \$415,454 7.8

223 \$108,386 \$94,304 \$39,040 \$43,631 \$46,513 \$84,167 \$416,042 8.2

235 \$108,407 \$94,321 \$39,066 \$44,108 \$46,536 \$84,187 \$416,626 8.7

247 \$108,426 \$94,337 \$39,090 \$44,525 \$46,557 \$84,206 \$417,141 9.1

Baseline Operating Cost: \$455,125

Minimum CHP Operating Cost: \$421,124

CHP Annual Savings: \$34,001

Minimum Simple Payback: 6.0 years

Monthly On Site Generation: 62,100 kWh

Annual On Site Generation (75% run time): 731,177 kWh

"Ideal" Generator Capacity: 111 kW

### Print: Method 3 Intermediate Results

HUD CHP Feasibility Screening Tool

\<\< Sample Data \>\>

Details of Method 3 Calculations:

For Philadelphia, Pennsylvania there are:

5,151 heating degree days

1,188 cooling degree days

and the average temperature is 54.1 F

Air conditioning consumes 0.974 kWh/sq ft per year

and space heating consumes 38,570 Btu/sq ft per year

Estimated annual thermal loads:

a\. space heating 2,835 MMBtu

b\. air conditioning (95,468 kWh) 1,909 MMBtu

c\. potable hot water 1,874 MMBtu

d\. total thermal load 6,618 MMBtu

CHP System

a\. generator capacity 51 kW

b\. heat rate 11,907 Btu/kWh

c\. heat recovery rate 6,234 Btu/kWh

d\. CHP system installed cost \$2,801/kW

e\. generator O&M cost \$0.019/kWh

CHP System Economics

a\. electricity Baseline CHP

1\. non-cooling power 346,920 346,920 kWh

2\. cooling power 95,468 95,467 kWh

3\. total power consumed 442,388 442,387 kWh

4\. on site generation 0 331,790 kWh

5\. utility power 442,338 110,597 kWh

b\. natural gas

1\. space heating 3,779 3,520 MMBtu

2\. potable hot water 2,498 0 MMBtu

3\. generator fuel 0 3,950 MMBtu

4\. total fuel consumed 6,277 7.470 MMBtu

c\. operating costs

1\. utility power \$52,069 \$13,017

2\. natural gas \$82,924 \$98,684

3\. generator O&M \$0 \$6,329

4\. total operating cost \$134,993 \$118,030

d\. simple payback 8.34 years

Space Heating Summary Hot Water Summary

a\. load 2,835 MMBtu a. load 1,874 MMBtu

b\. recovered heat 195 MMBtu b. recovered heat 1,874 MMBtu

c\. boiler load 2,640 MMBtu c. water heater load 0 MMBtu

d\. boiler fuel 3,520 MMBtu d. water heater fuel 0 MMBtu

Space Cooling Summary

a\. chilled water load 1,146 MMBtu

b\. thermal input 1,909 MMBtu

c\. recovered heat 0 MMBtu

d\. absorption chiller output 0 MMBtu

e\. electric chiller load 1,146 MMBtu

f\. cooling power 95,468 kWh

HUD CHP Feasibility Screening Tool

\<\< Sample Data \>\>

Method 3 Assumptions & Methodology:

1\. Space Heating and Cooling loads computed using EIA algorithms based
on Heating

and Cooling Degree Days

2\. Domestic Hot Water loads computed from hot water consumption
reported in ASHRAE

and average annual temperature for the location

3\. The generator is sized to provide 3/4 of the annual power
consumption with

a fraction of run time of 75%. It is assumed that peak power demand
occurs during

the time when the remaining 1/4 of the power is consumed.

4\. Heat recovered from the generator is allocated to thermal loads to
domestic

(potable) hot water, space heating, and space cooling, in that order.

5\. Ideally, there should be an iteration on generator capacity. This is
not

necessary as long as the application is limited by the electrical loads.
If

the thermal loads constrain the analysis, the cooling power listed in
the

box above will be different than the cooling power listed in line 2 to
the

left. The control logic has not been developed to iterate on the

generator capacity until the cooling power in line 2 equals the power

required by electric air conditioners supplementing the absorption
chiller

(the cooling power listed above).

## Data Menu

The "Data Menu" can be used to clear the form so new data can be entered
(identical action as "File" "New") or to fill in the form with a sample
set of data. The "Alt" key works as it does in the file menu with
"Alt-D" displaying the data menu, "Alt-D-C" clearing the form, and
"Alt-D-D" filling in entries for a sample data set.

The user should be aware of the fact that the sample data provided is
not particularly current and the results will appear more attractive
than are likely with current utility costs, particularly for natural
gas.

![](media/image12.jpeg){width="6.000694444444444in"
height="0.7611111111111111in"}

Figure 8 --- Data menu items.

## Help Item

The "Help" item is currently disabled, which allows revisions to the
compiled HELP file outside of re-installing the tool. The compiled HELP
file should be downloaded separately (see the website), and it should
run all by itself in a separate window. The compiled HELP file is
similar to this manual.

![](media/image13.jpeg){width="6.000694444444444in" height="0.69375in"}

Figure 9 --- Help item does not function.

# Electric Generation and Prime Movers

> CHP systems primarily consist of an engine-driven generator and heat
> recovery equipment. The system can include an absorption chiller that
> uses recovered heat to produce chilled water for air conditioning.
> Several types of equipment can be used to produce electricity:

-   reciprocating engines

-   gas turbines

-   microturbines

-   fuel cells

Electric power produced is usually consumed on site, although in some
circumstances it is economical to produce power that is exported to the
utility grid (though many prospective users would like to sell power to
the grid this is rarely in their best interest with utilities buying
power only at their own avoided cost).

Reciprocating engines and gas turbines are established technologies for
on site power generation and CHP. Microturbines have been commercially
available since the late 1990's with several thousand units installed
and operating. Fuel cells have attracted a great deal of attention as
candidate systems for on site power generation, but as of 2005 there are
few products on the market and installations number in the dozens
instead of hundreds or thousands. Fuel cells remain the most expensive
option for on-site generation and CHP, and are not covered in this
manual, although they can still be selected as a system in the tool if
one wants to see some cost or other data displayed (paybacks are often
negative or thousands of years).

## Reciprocating Engine Generators

Natural gas-fired reciprocating engines dominate the market for small
on-site generators and CHP systems. While microturbines may appear a
more glamorous technology, recips churn along as the established player
in these applications, with low cost, high efficiency, and long
durability. Also, gas turbines are only for larger applications (1,000
kW or more).

### Equipment Cost 

Correlations were developed based on data for generator cost (equipment
only), typical installation cost, operating and maintenance (O&M) costs,
efficiency, and heat recovery in the U.S. DOE Office of Energy
Efficiency and Renewable Energy report *Gas-Fired Distributed Energy
Resource Technology Characterizations*, NREL-TP-620-34783, 2003 (EERE
report cited in the rest of this section). Equipment costs are very
nearly linear in absolute terms, as shown by the blue dashed lines in
Figure 14, but highly non-linear in terms of cost per unit capacity.
There is a strong economy of scale favoring larger units. The portion of
the figure on the left expands the scale for 0 -- 300 kW.

![](media/image14.wmf){width="6.500694444444444in"
height="2.3270833333333334in"}

Figure 10 --- Reciprocating engine generator equipment cost, two scales.

### Installation Cost 

Installation costs of any CHP system will be highly dependent on
site-specific factors with any retrofit installation being much more
difficult and costly than systems put into new construction of buildings
designed to use CHP. Difficult installations can cost 2.5 times easy
installations, or more. That being said, the EERE report cites
installation costs for reciprocating-engine based CHP systems at 17% of
the total installed cost. This fraction is lower than values cited in
many other sources and has been associated with the "Low" setting under
"Installation Costs" on the "Intermediate Information" tab. Values of
25%, 50%, and 100% are associated with the "Typical," "High," and
"Retrofit" selections of "Installation Costs" for reciprocating engine
CHP systems.

### ![](media/image15.wmf){width="4.0in" height="2.9429133858267718in"}Heat Rate and Efficiency 

The same source was used to correlate engine efficiency in terms of the
fuel requirements. The natural gas consumed per unit of power generated,
the heat rate (Btu/kWh, HHV), was correlated against the engine
capacity. As illustrated by the blue dashed line in Figure 15, less fuel
is consumed per unit of output as generator capacity increases. In other
words, larger generators are typically more efficient than smaller ones
(red line).

### ![](media/image16.wmf){width="4.0in" height="2.858267716535433in"}Heat Recovery

Data from the EERE report were also used to correlate engine heat
recovery against generator capacity. Graphs from this correlation are
shown in Figure 16 with the blue line indicating the heat recovery rate
(Btu/kWh generated per hour) and the red line the absolute recovered
heat (Btu). Although more heat is available from larger generators,
since they are also more efficient less heat can be recovered per unit
of power output. Heat recovery rate declines as capacity increases.

### Operating and Maintenance Costs 

![](media/image17.wmf){width="3.8019685039370077in"
height="2.4811023622047244in"}Finally, the EERE report was used to
correlate O&M costs against generator capacity. A graph from this
correlation is shown in Figure 17 with the blue line indicating that
non-fuel operating costs decline as generator capacity increases. This
results from fixed maintenance costs being prorated over a greater
quantity of power output.

## Gas Turbine Generators

![](media/image18.wmf){width="4.0in"
height="2.8866141732283466in"}Natural gas-fired combustion gas turbines
can be used in larger on-site generation and CHP applications. These
machines resemble jet engines used on civilian and military aircraft,
though they have been designed for optimal torque and durability instead
of maximum thrust and low weight. Electrical capacities of gas turbine
generators range from about 750 kW to 40 MW, with only the smallest
machines being appropriate for most commercial building and residential
applications. Gas turbines typically have lower efficiencies than
reciprocating-engine driven generators, though they also have lower
maintenance costs and greater potential for waste heat recovery.

### Equipment Cost

Correlations were developed based on data for generator cost (equipment
only), typical installation cost, operating and maintenance (O&M) costs,
efficiency, and heat recovery in the EERE report. Equipment costs are
very nearly linear in absolute terms, as shown by the blue dashed line
in Figure 18, but highly non-linear in terms of cost per unit capacity.
There is a strong economy of scale favoring larger units.

### Installation Cost 

The EERE report cites installation costs for gas turbine based CHP
systems at 15% of the total installed cost. This fraction is lower than
values cited in many other sources and has been associated with the
"Low" setting under "Installation Costs" on the "Intermediate
Information" tab. Values of 25%, 50%, and 100% are associated with the
"Typical," "High," and "Retrofit" selections of "Installation Costs" for
gas turbine CHP systems. 

### ![](media/image19.wmf){width="4.3in" height="3.08740157480315in"}Heat Rate and Efficiency 

The same source was used to correlate turbine efficiency in terms of the
fuel requirements. The natural gas consumed per unit of power generated,
the heat rate (Btu/kWh), was correlated against the engine capacity. As
illustrated by the blue dashed line in Figure 19, less fuel is consumed
per unit of output as generator capacity increases. In other words,
larger generators are typically more efficient than smaller ones (red
line).

### Heat Recovery 

![](media/image20.wmf){width="4.285433070866142in"
height="3.293700787401575in"}Data from the EERE report were also used to
correlate engine heat recovery against generator capacity. Graphs from
this correlation are shown in Figure 20 with the red line indicating the
absolute heat recovery rate (millions of Btu's per hour) and the dashed
blue line the recovered heat per unit of power generated (Btu/kWh).
Although more heat is available from larger generators, since they are
also more efficient, less heat can be recovered per unit of power
output. Heat recovery rate declines as capacity increases.

### Operating and Maintenance Costs 

![](media/image21.wmf){width="4.0in"
height="3.0661417322834645in"}Finally, the EERE report was used to
correlate O&M costs against generator capacity. A graph from this
correlation is shown in Figure 21 with the blue line indicating that
non-fuel operating costs decline as generator capacity increases. This
results from fixed maintenance costs being prorated over a greater
quantity of power output.

## Microturbine Generators

![](media/image22.wmf){width="4.0in"
height="2.858267716535433in"}Microturbines are a relatively new
generator technology that can be used in small to medium-sized on-site
generation and CHP applications. Electrical capacities of microturbines
range from 30 to 200 kW. Microturbines typically have lower efficiencies
and are expected to have low maintenance costs (since they are fairly
new products, microturbines are still establishing a track record for
O&M costs and reliability).

### Equipment Cost 

Correlations were developed based on data for generator cost (equipment
only), typical installation cost, operating and maintenance (O&M) costs,
efficiency, and heat recovery in the EERE report. Equipment costs are
very nearly linear in absolute terms, as shown by the dashed blue line
in Figure 22, but highly non-linear in terms of cost per unit capacity.
There is a strong economy of scale favoring larger units.

### Installation Cost 

![](media/image23.wmf){width="4.0in" height="2.6980314960629923in"}The
EERE report cites installation costs for gas turbine based CHP systems
at 18% of the total installed cost. This fraction is lower than values
cited in many other sources and has been associated with the "Low"
setting under "Installation Costs" on the "Intermediate Information"
tab. Values of 25%, 50%, and 100% are associated with the "Typical,"
"High," and "Retrofit" selections of "Installation Costs" for
microturbine CHP systems.

### Heat Rate and Efficiency 

The same source was used to correlate engine efficiency in terms of the
fuel requirements. The natural gas consumed per unit of power generated,
the heat rate (Btu/kWh), was correlated against the engine capacity. As
illustrated by the dashed blue line in Figure 23, less fuel is consumed
per unit of output as generator capacity increases. In other words,
larger generators are slightly more efficient than smaller ones (red
line).

### ![](media/image24.wmf){width="4.0in" height="2.952755905511811in"}Heat Recovery 

Data from the EERE report were also used to correlate engine heat
recovery against generator capacity. Graphs from this correlation are
shown in Figure 24 with the dashed blue line indicating the absolute
heat recovery rate (millions of Btu's per hour) and the red line the
recovered heat per unit of power generated (Btu/kWh). Although more heat
is available from larger generators, since they are also more efficient,
less heat can be recovered per unit of power output. Heat recovery rate
declines as capacity increases.

### Operating and Maintenance Costs 

![](media/image25.wmf){width="3.4956692913385825in"
height="2.6956692913385827in"}Finally, the EERE report was used to
correlate O&M costs against generator capacity. A graph from this
correlation is shown in Figure 25 with the dashed blue line indicating
that non-fuel operating costs decline as generator capacity increases.
This results from fixed maintenance costs being prorated over a greater
quantity of power output.

# Algorithms and Methodology

The HUD CHP Tool employs three distinctly different algorithms for
estimating operating characteristics and economics for CHP systems.
"Method 1" allows for use of recovered heat only for producing domestic
hot water. "Method 2" uses a complicated process for sizing a CHP system
that uses recovered heat for space heating, domestic hot water and
chilled water using an absorption chiller. "Method 3" estimates the
annual savings of operating a CHP system that uses a natural-gas driven
electric generator with heat recovery for domestic hot water, space
heating, and space cooling using an absorption chiller based on
published tables rather than utility bills.

## "Method 1" Algorithms

![](media/image26.jpeg){width="5.267322834645669in"
height="3.0in"}Method 1 estimates the annual savings from operating a
CHP system that produces electricity and uses recovered heat for
domestic (potable) hot water. It does not incorporate waste heat
recovery for either space heating or space cooling needs. Consequently,
this method generally results in a smaller generator capacity and a
longer simple payback than either Method #2 or Method #3. Monthly hot
water fuel consumption is calculated from the input data for building
fuel consumption that the user specified on the "Energy & Utility Data"
tab. It is computed as the average of the building fuel consumption for
the months May through September as illustrated in Figure 26.

Any fuel consumption in excess of this summertime monthly average is
assumed to be for space heating (see Figure 27) and is ignored in the
Method 1 analysis. Water heating fuel consumption is converted to
estimated hot water load by multiplying it by a fixed annual boiler
efficiency of 62% (there is an implicit assumption that the building
contains a hot water or steam boiler that provides both space heating
and domestic hot water needs and that there are significant hours at low
part load, and consequently low efficiency, operation). Boiler
efficiency can be specified in the "Misc. Input Information" tab though.

![](media/image27.wmf){width="5.988888888888889in"
height="3.4631944444444445in"}

Figure 11 --- Method 1 heating and hot water fuel breakout.

Method 1 scales the summer hot water load to an annual load (MMBtu) and
sizes the generator to provide that amount of recovered heat by
operating 7,440 hours per year (generator heat recovery is provided
across a range of capacities for reciprocating-engine driven generators,
gas turbine generators, microturbines, and fuel cells). Annual costs for
electricity and natural gas are calculated using user input data from
the utility rate information (i.e. energy charge, fuel adjustment
charge, demand charge, standby charge, and cost of natural gas) from the
"Energy & Utility Data" tab and monthly peak demand from the monthly
utility billing data. Gen-set equipment and operating and maintentance
costs (O&M) are provided from the curves shown previously.

Details of the Method 1 analysis can be displayed on a separate "tab" by
clicking the box for "Show Details for Method 1" on the "Results" tab of
the data interface (Figure 28).

![](media/image28.wmf){width="5.988888888888889in"
height="4.665972222222222in"}

Figure 12 --- Method 1 results tab.

## "Method 2" Algorithms

Method 2 allows selection of three end-use heat recovery options:

-   Space Heating & Domestic Hot Water Only (No Cooling)

-   Heating & Cooling With Priority to Heating

-   Heating & Cooling with Priority to Cooling

Hot water fuel can also be specified if multiple fuels are used. Method
2 is the most complicated.

### Method 2 Assumptions & Methodology:

1\. Fuel Use for Space Heating and Hot Water

a\. load derived from fuel use input data on "Monthly Utility Data" tab

b\. default assumes boiler/water heater efficiency of 62%

c\. hot water load set at load for Method 1

2\. Space Cooling Load and Energy Use

a\. load derived from input data for electrical power use for winter
months on

"Monthly Utility Data" tab

b\. electrical a/c efficiency assumed to be SEER 12

c\. absorption chiller efficiency assumed to be gCOP 0.60 for "low
temperature" heat for

recip engines, microturbines, and fuel cells; 1.20 for "high
temperature" exhaust from

gas turbines

3\. Cost of Power

a\. uses specific input data for energy consumption, fuel adjustment
charge, demand charge,

and standby charge on "Monthly Utility Data" and "Utility Rate Data"
tabs

b\. input data for monthly electric bills is not used

c\. average cost of power displayed on "Monthly Utility Data" tab is not
used

4\. Cost of Fuel

a\. specific input data for cost of natural gas on "Utility Rate Data"
tab is used for

generator fuel

b\. either natural gas cost or average cost of Fuel #1 from "Monthly
Utility Data" tab is

used for water heater fuel (default is natural gas, selection is made on
"Method 2" tab)

5\. On-Site Power Generation

a\. selected to give lowest simple payback

b\. assumes each month has the same generation up to the actual monthly
consumption

specified on the "Monthly Utility Data" tab

6\. Generator Size & Characteristics

a\. sized for 75% on-time by default, user selectable on "Misc. Input
Information"

b\. cost and performance taken from curve fits

### Method 2 Results

Details of the Method 2 analysis can be displayed on a separate "tab" by
clicking the box for "Show Details for Method 2" on the "Results" tab of
the data interface, as shown in Figure 29. The table in the middle of
the form contains intermediate results of the calculations for a single
month, August, for the first 10 out of 20 or so generator sizes
considered. The particular month that is displayed can be changed using
the leftmost of the two scroll bars in the upper-right corner of the
form. The range of generator sizes displayed can be changed using the
rightmost scroll bar. The optimum generator size is in bold.

There are several option boxes at the top of the form, and a button
labeled "View Payback Graph." The "View Payback Graph" button can be
used to display a graph showing simple paybacks across a range of
generator capacities. The summary results are displayed in the table at
the top of the form. The options boxes allow specification of recovered
heat allocation (top left) and water heating fuel.

Assumptions and methodology items are also displayed in the scroll box
at bottom right, except boiler/water heater efficiency and generator
runtimes may be different than shown.

![](media/image29.jpeg){width="6.4944444444444445in" height="3.3375in"}

Figure 13 --- Method 2 results tab.

Each row of the intermediate results table in the middle shows results
for a fixed output level from a hypothetical generator, ranging from 0
kWh (i.e. no on-site generation) to the maximum electrical load for any
month in the year (from the input data on the "Monthly Utility Data"
tab). Corresponding rows for each month of the year are added to create
the table at the bottom of the form. Clicking either end of the
rightmost scroll bar shifts the rows of this table up or down to see
results that are outside the range being displayed. The row of the table
that corresponds to the lowest simple payback (i.e. \[CHP system
equipment + installation cost\] ÷ \[Baseline Annual Operating Cost - CHP
System Annual Operating Cost\]) is shown in bold numbers (there is an
implicit assumption that generator output is constant from month to
month).

The intermediate result columns are:

-   a specified generator capacity (column 1)

-   the corresponding generator power output for the month (column 2)

-   the corresponding amount of recovered heat (column 3) is computed
    from generator characteristics (Btu/kWh generated) and the assumed
    gen-set output in column 2

-   the amounts of recovered heat allocated to space heating and
    domestic hot water (column 4)

-   the output from a boiler or water heater (column 5)

-   recovered heat allocated to an absorption chiller (column 6)

-   chilled water produced from a recovered heat "fired" absorption
    chiller (column 7)

-   cooling produced by an electric air conditioning system to meet any
    load not satisfied by a recovered heat fired chiller (column 8)

-   total power consumption (column 11)

-   space heating and hot water load is computed from input data for
    monthly fuel consumption ("Monthly Utility Data" tab) and a fixed
    boiler efficiency (i.e. 62% as an annual average

-   the available recovered heat is allocated between heating and
    cooling needs (columns 3 and 5 in Fig. 1) with priority given either
    to heating needs or cooling needs based on the "radio" buttons in
    the upper left of the form (the display is slightly different if
    "priority chilled water" is selected):

-   recovered heat is given to heat and hot water up to their combined
    load with anything left over given to an absorption chiller
    (priority heating) as displayed in Fig. 1.

-   recovered heat is given to an absorption chiller up to the amount
    needed to satisfy the cooling load for that month with anything left
    over allocated to domestic hot water or heating (priority chilled
    water); this calculation incorporates assumed efficiencies for both
    the hypothetical or proposed absorption chiller (0.60 for CHP using
    generators with reciprocating engines, microturbines, or fuel cells
    and 1.20 for CHP systems using gas turbines) and the actual electric
    air conditioners (EER 12).

-   water heater output, column 4, is the difference between the hot
    water load and recovered heat allocated to heating and hot water.

-   absorption and electric chiller outputs, columns 7 and 8, are
    determined from the heat into the absorption chiller and the total
    cooling load

-   electrical power for cooling, column 9, is computed from the
    necessary electric a/c output using an EER of 12

-   non-cooling power, column 10, is set from the input for monthly
    power consumption

-   total power, column 11, and purchased utility power, column 11, are
    calculated as the sum of cooling power and non-cooling power, and
    the difference between total power, column 10, and CHP system
    generator output, column 1

-   gen-set fuel, column,13 water heater fuel, colum 14, and total fuel
    consumption, column 15, are calculated from a curve fit for
    generator and the assumed boiler efficiency (62%)

-   the cost of power, column 16, is computed as the sum of:

-   the purchased utility power (column 12) times the electric utility
    energy charge plus fuel adjustment charge ("Monthly Utility Data"
    tab),

-   the demand charge times the monthly peak electrical demand ("Monthly
    Utility Data" tab) less the generator electrical capacity, and

-   the standby charge ("Monthly Utility Data" tab) times the generator
    capacity.

-   the cost of fuel, column 17, is computed using generator (column 13)
    and water heater (column 14) fuel consumption, input data for the
    cost of natural gas ("Monthly Utility Data" tab) for generator fuel
    consumption and either the average annual cost of fuel #1 ("Monthly
    Utility Data" tab) or the cost of natural gas for water heater fuel
    depending on the choice for water heater fuel ("radio" button next
    to choices for recovered heat allocation.

-   total utility cost, column 18, is the sum of the cost of power and
    cost of fuel (columns 16 and 17)

-   genset O&M cost is the generator power output (column 2) times the
    gen-set O&M rate (\$/kWh generated)

-   monthly operating cost, column 19, is the sume of total utility
    (i.e. energy) costs and gen-set O&M costs

CHP equipment cost is computed from the generator capacity (column 1)
and curve fits for equipment and installation costs as functions of
generator size (e.g. Reciprocating Engine Generators).

## "Method 3" Algorithms

Method 3 estimates the annual savings of operating a CHP system that
uses a natural-gas driven electric generator with heat recovery for
domestic hot water, space heating, and space cooling using an absorption
chiller. Heating, cooling, and hot water loads are estimated from
published tables and algorithms; the monthly table of electric and gas
utility billing information on the "Energy & Utility Data" tab are not
used except for calculating electric utility peak demand charges, so
Method 3 results can be generated more easily and for a proposed design
(and without monthly utility data, only rate data).

End-use calculations are based on the following references:

-   space heating gas consumption: 2001 RECS, Table CE2-1c.
    Space-Heating Energy Consumption in U.S. Households by Climate Zone

-   space cooling power consumption: 2001 RECS, Table CE3-1c. Electric
    Air Conditioning Energy Consumption in U.S. Households by Climate
    Zone

-   non-cooling power: Ritschard, R.L., Huang, Y.J., and Fay, J.M.,
    "Estimating Water Heating and Aggregate Electricity Loads in
    Multifamily Buildings," ASHRAE Transactions 1990, Volume 96, Part
    1, p. 799.

-   hot water consumption: Goldner, F.S., "DHW System Sizing Criteria
    for Multifamily Buildings," ASHRAE Transactions 1994, Volume 100,
    Part 1, p. p74.

Source: 2001 RECS refers to the *2001 Consumption and Expenditures
Tables*, Residential Energy Consumption Surveys, available as PDF
documents from the US Dept of Energy, Energy Information Administration
website:

(main current URL: <http://www.eia.doe.gov/emeu/recs/contents.html>)

(2001 RECS CE URL:
<http://www.eia.doe.gov/emeu/recs/recs2001/detailcetbls.html>)

(CE2-1c table URL:
<ftp://ftp.eia.doe.gov/pub/consumption/residential/2001ce_tables/spaceheat_consump2001.pdf>)

(CE3-1c table URL:
<ftp://ftp.eia.doe.gov/pub/consumption/residential/2001ce_tables/ac_consump2001.pdf>)

Baseline energy consumption for space heating is calculated using an
algorithm derived by the U.S. Department of Energy from the 2001 RECS.
Space heating "intensity" is correlated against heating and cooling
degree days (HDD and CDD) and climate zone for several different types
of space heating fuel. The correlations are summarized in the table
below. Fuel use per 1000 sq feet of heated floor space is computed using
input data for the building location and heated floor space on the
"Intermediate Information" tab. Fuel use converted to annual heating
load assuming a fixed boiler efficiency of 62%. The domestic hot water
load is computed using data published by ASHRAE. Non-cooling electric
loads are set to 3.54 kWh/yr/sq ft of heated floor space, with the floor
space taken from the user specified input data on the "Intermediate
Information" tab. Reference information:

  --------------------- ------------------------- --------- --------- ---------- ----------
  RECS 2001\                                                                     
  Table CE2-1c.                                                                  
  Space-Heating Energy                                                           
  Consumption in U.S.                                                            
  Households by Climate                                                          
  Zone                                                                           

  Space-Heating         Fewer than 2,000 CDD and                                 2,000 CDD\
  Intensity, Where the\ \--                                                      or More\
  Main Space-Heating                                                             and Fewer\
  Fuel Is:                                                                       than\
                                                                                 4,000 HDD

                        More than\                5,500 to\ 4,000 to\ Fewer      
                        7,000 HDD                 7,000 HDD 5,499 HDD than\      
                                                                      4,000 HDD  

                        Space-Heating Intensity                                  
                        \[PU÷{HDDx(HSF÷1000)}\]                                  

    Electricity (kWh)\  0.766\                    0.717\    0.834\    0.864\     0.998\
    Natural Gas (cubic  4.479\                    6.222\    8.291\    8.951\     8.969\
  feet)\                0.041\                    0.044\    0.051\    Q\         Q\
    Fuel Oil (gallons)\ 0.046\                    Q\        Q\        0.046\     Q\
    Kerosene (gallons)\ 0.061                     0.066     0.080     0.099      0.104
    LPG (gallons)                                                                

  Q = Data withheld                                                              
  because either the                                                             
  Relative Standard                                                              
  Error (RSE) was                                                                
  greater than 50% or                                                            
  fewer than 10                                                                  
  households were                                                                
  sampled.                                                                       
  --------------------- ------------------------- --------- --------- ---------- ----------

As an example, Albany, New York typically has 7,005 heating degree days
(HDD) and 776 cooling degree days (CDD) per year. Consequently, for a
building with 98,000 sq feet of heated space:

Natural Gas Consumption (cu ft) ÷ {7,005 HDD x (98,000 sq ft/1,000)} =
4.479

Natural Gas Consumption (cu ft) = 4.479 x 7,005 HDD x (98,000 sq ft/1000
sq ft) = 3,075,000 cu ft

Natural Gas Consumption = 3,075,000 cu ft x 1,027 Btu/cu ft x (1
MMBtu/1,000,000 Btu) = 3,158 MMBtu

Air-conditioning energy is also calculated using an algorithm published
by the U.S. Department of Energy. Air-conditioning "intensity" is
correlated against heating and cooling degree days (HDD and CDD) for
central and room air-conditioners as summarized in the table below.
Annual power consumption is determined using input data for the location
and heated and air-conditioned floor space specified on the
"Intermediate Information" tab. The annual cooling load is calculated
assuming an electric air-conditioner EER of 12 Btu/Wh.

  ------------------------ -------------------------- --------- -------- --------- ----------
  2001 RECS\                                                                       
  Table CE3-1c. Electric                                                           
  Air-Conditioning Energy                                                          
  Consumption in U.S.                                                              
  Households by Climate                                                            
  Zone, 2001                                                                       

  Space-Heating Intensity, Fewer than 2,000 CDD and                                2,000 CDD\
  Where the\               \--                                                     or More\
  Main Space-Heating Fuel                                                          and Fewer\
  Is:                                                                              than\
                                                                                   4,000 HDD

                           More than\                 5,500 to\ 4,000    Fewer     
                           7,000 HDD                  7,000 HDD to\      than\     
                                                                5,499    4,000 HDD 
                                                                HDD                

                           Air-Conditioning Intensity                              
                           \[kWh÷{CDDx(CSF÷1000)}\]                                

    Electric Air           0.80\                      0.78\     0.81\    0.88\     0.90\
  Conditioning\            0.78\                      0.78\     0.82\    0.85\     0.90\
      Central              0.85                       0.75      0.77     1.07      0.79
  Air-Conditioning\                                                                
      Room/Wall                                                                    
  Air-Conditioning                                                                 
  ------------------------ -------------------------- --------- -------- --------- ----------

Continuing the Albany example:

Central Air Conditioning Power (kWh) ÷ {776 CDD x (98,000 sq ft/1,000 sq
ft)} = 0.78

Central Air Conditioning Power (kWh) = 0.78 x {776 CDD x (98,000 sq ft /
1,000 sq ft)} = 59,320 kWh

Annual Air Conditioning Load (ton-hrs) = 59,320 kWh x 12 Btu/Wh x 1,000
Wh/kWh ÷ 12,000 Btu/ton-hr = 59,320 ton-hrs

Results of the Method 3 and intermediate calculations are displayed on
the "Method 3" results tab (Figure 30). The text box can be used to
change the default "Central A/C" selection to "Room/Wall A/C" to select
a different row of air-conditioning intensity values for the
calculations. Space heating calculations are performed using the row of
space heating intensity factors for natural gas.

Method 3 is based on simplified estimating calculations, so calculated
savings and simple paybacks for Method 3 can be more inaccurate in some
cases where the "averaging" assumptions do not represent the building
well. Method 3 is more suited to quick, conceptual scoping estimates
when energy data are not yet available.

### ![](media/image30.wmf){width="5.988888888888889in" height="5.2243055555555555in"}

Figure 14 --- Method 3 results tab.

### Details of Method 3 Calculations using the Sample Data:

For Philadelphia, Pennsylvania there are:

5,151 heating degree days

1,188 cooling degree days

and the average temperature is 54.1 F

Air conditioning consumes 0.974 kWh/sq ft per year

and space heating consumes 38,570 Btu/sq ft per year

Estimated annual thermal loads:

a\. space heating 2,835 MMBtu

b\. air conditioning (95,468 kWh) 1,909 MMBtu

c\. potable hot water 1,874 MMBtu

d\. total thermal load 6,618 MMBtu

CHP System

a\. generator capacity 51 kW

b\. heat rate 11,907 Btu/kWh

c\. heat recovery rate 6,234 Btu/kWh

d\. CHP system installed cost \$2,801/kW

e\. generator O&M cost \$0.019/kWh

CHP System Economics

a\. electricity Baseline CHP

1\. non-cooling power 346,920 346,920 kWh

2\. cooling power 95,468 95,467 kWh

3\. total power consumed 442,388 442,387 kWh

4\. on site generation 0 331,790 kWh

5\. utility power 442,338 110,597 kWh

b\. natural gas

1\. space heating 3,779 3,520 MMBtu

2\. potable hot water 2,498 0 MMBtu

3\. generator fuel 0 3,950 MMBtu

4\. total fuel consumed 6,277 7.470 MMBtu

c\. operating costs

1\. utility power \$52,069 \$13,017

2\. natural gas \$82,924 \$98,684

3\. generator O&M \$0 \$6,329

4\. total operating cost \$134,993 \$118,030

d\. simple payback 8.34 years

Space Heating Summary Hot Water Summary

a\. load 2,835 MMBtu a. load 1,874 MMBtu

b\. recovered heat 195 MMBtu b. recovered heat 1,874 MMBtu

c\. boiler load 2,640 MMBtu c. water heater load 0 MMBtu

d\. boiler fuel 3,520 MMBtu d. water heater fuel 0 MMBtu

Space Cooling Summary

a\. chilled water load 1,146 MMBtu

b\. thermal input 1,909 MMBtu

c\. recovered heat 0 MMBtu

d\. absorption chiller output 0 MMBtu

e\. electric chiller load 1,146 MMBtu

f\. cooling power 95,468 kWh

### Method 3 Assumptions & Methodology Applied to the Sample Data

1\. Space Heating and Cooling loads computed using EIA algorithms based
on Heating and Cooling Degree Days

2\. Domestic Hot Water loads computed from hot water consumption
reported in the ASHRAE papers cited above, and average annual
temperature for the location

3\. The generator is sized to provide 3/4 of the annual power
consumption with a fraction of run time of 75%. It is assumed that peak
power demand occurs during the time when the remaining 1/4 of the power
is consumed. (Generator runtime can be changed on the "Misc. Input
Information" tab.)

4\. Heat recovered from the generator is allocated to thermal loads to
domestic (potable) hot water, space heating, and space cooling, in that
order.

5\. Ideally, there should be an iteration on generator capacity. This is
not necessary as long as the application is limited by the electrical
loads. If the thermal loads constrain the analysis, the cooling power
listed in the box above will be different than the cooling power listed
in line a.2, CHP System Economics, to the left. The control logic has
not been developed to iterate on the generator capacity until the
cooling power in line 2 equals the power required by electric air
conditioners supplementing the absorption chiller (the cooling power
listed above).

# Additional Information on Building Loads

## Electrical & Thermal Loads

The CHP calculations require information about the space heating, hot
water, and space cooling loads of the building. The HUD CHP Tool
performs three different estimates for CHP using different assumptions
about the use of recovered heat and algorithms for estimating these
loads. These methods include CHP systems:

-   employing recovered heat to produce domestic hot water using the
    billing information on Energy & Utility Data to estimate monthly and
    annual hot water loads.

-   employing recovered heat for space heating, domestic hot water, and
    space cooling using the billing information on Energy & Utility Data
    to estimate monthly and annual hot water loads.

-   employing recovered heat for space heating, domestic hot water, and
    space cooling using information specified by the user on the
    Intermediate Information tab for the building location, approximate
    numbers of heated and cooled square feet, the approximate number of
    people living in the building, and "high," "medium," or "low" hot
    water usage.

Additional information about these calculations is available under the
headings for "Electrical Loads" and "Space Heating & Hot Water Loads".

## Electrical Loads 

The power consumption data from the utility bills (see Energy & Utility
Data) is used to estimate the air conditioning power consumption and
space cooling loads. Figure 31 illustrates how this is done in the HUD
CHP Tool. It shows the power consumption for each month with a
horizontal line indicating the average power for the winter months.

![](media/image31.jpeg){width="5.188888888888889in"
height="2.995833333333333in"}

Figure 15 --- Monthly power consumption and average winter power use.

The average power use during the winter is assumed to be almost entirely
lighting and plug loads, and does not include any power for air
conditioners. The plug and lighting loads are assumed to be constant
throughout the year, so any electrical use during the summer months in
excess of this average is for air conditioning. This is illustrated in
Figure 32.

![](media/image32.jpeg){width="5.188888888888889in"
height="2.995833333333333in"}

Figure 16 --- Breakout of air conditioning energy.

Air conditioning power consumption is converted to monthly air
conditioning loads by multiplying the power use by an assumed air
conditioning efficiency (EER) of 12 Btu/kWh. The loads in millions of
Btu's per month are needed in order to estimate recovered heat
requirements of an absorption chiller to provide air conditioning. An
absorption chiller uses heat, instead of electrical energy, to produce
44°F water for space cooling. CHP systems using reciprocating-engine or
microturbine generators or fuel cells produce low grade waste heat that
can drive an absorption chiller with a COP of 0.60; gas turbines have
much higher exhaust gas flows and temperatures and can operate chillers
with COPs of 1.20.

## Space Heating & Hot Water Loads 

Space heating and hot water loads are also estimated using the data on
the Energy & Utility Data data form. (See figures 26 and 27).

The HUD CHP Tool allows for use of up to two different fuels (e.g.
natural gas and #2 fuel oil). Each value is converted from its customary
units of measure (e.g. gallons, thousands of cubic feet) to millions of
Btu's using the appropriate conversion factors. The two values are added
for each month to get a total "thermal" consumption and converted to
heating and hot water loads by multiplying by the annual boiler
efficiency (default of 60%, which includes distribution and standby
losses). Boiler annual efficiency can be set on the "Misc. Input
Information" tab.

## ![](media/image33.jpeg){width="5.0in" height="3.8583333333333334in"}Map of EIA Climate Zones for 2001 RECS