ASHRAE Journal - April 2013 - 15

Large Heat Pump/Small Storage Tank

Small Heat Pump/Large Storage Tank

Heat Pump Capacity

310 kBtu/h

90 kBtu/h

Storage Tank Capacity

120 gallon

720 gallon

Power Input (Varies with GHX Temperature)

36 kW

11 kW

Recovery Time

0.30 hours

5.7 hours

Table 1: This table summarizes the design of alternative approaches to produce DHW for a typical apartment building using a
GCHP system.

Table 2A: Monthly peak heating and cooling loads (kBtu) and monthly energy loads (kBtu/h) for a typical apartment building.
Table 2B: Monthly peak heating and cooling loads and monthly energy loads with DHW heating loads assuming a 120 gallon
(454 L) storage tank is used. Table 2C: Monthly peak heating and cooling loads and monthly energy loads with DHW loads assuming a 720 gallon (2,725 L) storage tank is used.
implications on the size of your electricity bill if your home
has a smart meter measuring peak electrical demand as well
as consumption.
TES has implications for your electric utility. The size of
generating stations, distribution grid and transformers needed
to get energy to your home, and with some utilities even the
type of fuel used to generate electricity, are all impacted by
your decisions.

Domestic Hot Water Storage Tanks in a GCHP Application
Many facilities have predictable and intermittent domestic hot water (DHW) requirements. Occupants in apartment
buildings tend to use hot water heavily for a few hours in the
morning before heading to work and a few hours in the evening preparing and cleaning up after dinner.
When designing a DHW system using a gas boiler or gas
water heaters, there is little impact on the capital cost on the
system. It may cost less to increase the capacity of the boiler
and decrease the storage tank size when space in the mechanical room is limited. The following example illustrates the impact of TES on a GCHP system.
A typical apartment building was selected to illustrate
the impact of DHW production using a large heat pump/
small storage tank compared to a small heat pump/large
storage capacity combination. The following assumptions
April 2013

were used to calculate heat pump and storage tank capacity
(Table 1):
• 84 showers over two hours consuming 966 gallons (3657
L) of water between 6 and 8 a.m., plus 483 gallons (1828 L)
between 6 and 8 p.m.;
• Makeup water temperature: 55°F (12.8°C); and
• Water temperature to showers: 110°F (43°C).
An energy model was created for the project and DHW
loads were added to create three sets of loads:
• Building heating and cooling only;
• Heating and cooling with 310 kBtu/h (90.0 kW) heat
pump /120 gallon (454 L) storage capacity; and
• Heating and cooling with 90 kBtu/h (26.4 kW) heat
pump/720 gallon (2725 L) storage capacity.
Monthly peak heating and cooling loads and monthly energy
loads derived from the energy models are shown in Table 2.
These were used to calculate size of the GHX for the alternatives using commercially available GHX design software using “g” functions (non-dimensional temperature factors that
calculate a borehole field response to heat injection and heat
extraction pulses).
The length of the boreholes was calculated using the following parameters. Results are summarized in Table 3.
• Grid of five boreholes by four boreholes with 20 ft (6.1 m)
spacing between boreholes;
ASHRAE Journal

15



ASHRAE Journal - April 2013

Table of Contents for the Digital Edition of ASHRAE Journal - April 2013

ASHRAE Journal - April 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Ground-Coupled Heat Pump and Energy Storage
Fan Efficiency Requirements for Standard 90.1-2013
Technology Award Case Studies:
Geothermal for 5 Ecosystems
Holistic HVAC Design
Standing Columns
Engineer’s Notebook
Data Centers
Emerging Technologies
IAQ Applications
Refrigeration Applications
Special Products
People
International Column
Energy Modeling
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2013 - ASHRAE Journal - April 2013
ASHRAE Journal - April 2013 - Cover2
ASHRAE Journal - April 2013 - 1
ASHRAE Journal - April 2013 - 2
ASHRAE Journal - April 2013 - Contents
ASHRAE Journal - April 2013 - Commentary
ASHRAE Journal - April 2013 - 5
ASHRAE Journal - April 2013 - Industry News
ASHRAE Journal - April 2013 - 7
ASHRAE Journal - April 2013 - 8
ASHRAE Journal - April 2013 - Letters
ASHRAE Journal - April 2013 - Meetings and Shows
ASHRAE Journal - April 2013 - 11
ASHRAE Journal - April 2013 - 12
ASHRAE Journal - April 2013 - 13
ASHRAE Journal - April 2013 - Ground-Coupled Heat Pump and Energy Storage
ASHRAE Journal - April 2013 - 15
ASHRAE Journal - April 2013 - 16
ASHRAE Journal - April 2013 - I1
ASHRAE Journal - April 2013 - I2
ASHRAE Journal - April 2013 - I3
ASHRAE Journal - April 2013 - I4
ASHRAE Journal - April 2013 - 17
ASHRAE Journal - April 2013 - 18
ASHRAE Journal - April 2013 - 19
ASHRAE Journal - April 2013 - 20
ASHRAE Journal - April 2013 - 21
ASHRAE Journal - April 2013 - 22
ASHRAE Journal - April 2013 - 23
ASHRAE Journal - April 2013 - Fan Efficiency Requirements for Standard 90.1-2013
ASHRAE Journal - April 2013 - 25
ASHRAE Journal - April 2013 - 26
ASHRAE Journal - April 2013 - 27
ASHRAE Journal - April 2013 - 28
ASHRAE Journal - April 2013 - 29
ASHRAE Journal - April 2013 - 30
ASHRAE Journal - April 2013 - 31
ASHRAE Journal - April 2013 - Geothermal for 5 Ecosystems
ASHRAE Journal - April 2013 - 33
ASHRAE Journal - April 2013 - 34
ASHRAE Journal - April 2013 - 35
ASHRAE Journal - April 2013 - 36
ASHRAE Journal - April 2013 - 37
ASHRAE Journal - April 2013 - 38
ASHRAE Journal - April 2013 - 39
ASHRAE Journal - April 2013 - Holistic HVAC Design
ASHRAE Journal - April 2013 - 41
ASHRAE Journal - April 2013 - 42
ASHRAE Journal - April 2013 - 43
ASHRAE Journal - April 2013 - 44
ASHRAE Journal - April 2013 - 45
ASHRAE Journal - April 2013 - 46
ASHRAE Journal - April 2013 - 47
ASHRAE Journal - April 2013 - Engineer’s Notebook
ASHRAE Journal - April 2013 - 49
ASHRAE Journal - April 2013 - 50
ASHRAE Journal - April 2013 - 51
ASHRAE Journal - April 2013 - 52
ASHRAE Journal - April 2013 - 53
ASHRAE Journal - April 2013 - Data Centers
ASHRAE Journal - April 2013 - 55
ASHRAE Journal - April 2013 - 56
ASHRAE Journal - April 2013 - 57
ASHRAE Journal - April 2013 - 58
ASHRAE Journal - April 2013 - 59
ASHRAE Journal - April 2013 - Emerging Technologies
ASHRAE Journal - April 2013 - 61
ASHRAE Journal - April 2013 - 62
ASHRAE Journal - April 2013 - 63
ASHRAE Journal - April 2013 - IAQ Applications
ASHRAE Journal - April 2013 - 65
ASHRAE Journal - April 2013 - 66
ASHRAE Journal - April 2013 - Refrigeration Applications
ASHRAE Journal - April 2013 - Special Products
ASHRAE Journal - April 2013 - People
ASHRAE Journal - April 2013 - International Column
ASHRAE Journal - April 2013 - 71
ASHRAE Journal - April 2013 - Energy Modeling
ASHRAE Journal - April 2013 - 73
ASHRAE Journal - April 2013 - Products
ASHRAE Journal - April 2013 - 75
ASHRAE Journal - April 2013 - 76
ASHRAE Journal - April 2013 - 77
ASHRAE Journal - April 2013 - 78
ASHRAE Journal - April 2013 - Classified Advertising
ASHRAE Journal - April 2013 - Advertisers Index
ASHRAE Journal - April 2013 - Cover3
ASHRAE Journal - April 2013 - Cover4
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