ASHRAE Journal - April 2013 - 16

Heating and Cooling Only

DHW with Large Heat Pump/
Small Storage

DHW with Small Heat Pump/
Large Storage

Total Borehole

7,780 ft

7,880 ft

6,500 ft

Maximum Temperature

85.0°F

77.7°F

82.7°F

Minimum Temperature

39.1°F

32.0°F

32.0°F

Table 3: Total borehole length for GHX calculated for a five year prediction time to stay within a temperature range of 85°F
and 32°F (29.4°C and 0°C). Calculations are based on site specific data and vary by geology and geography. Calculations are
designed to illustrate relative GHX lengths for a project based on energy loads and peak heating loads added to a system when
DHW is added. Note that adding DHW loads to the GHX reduces minimum entering temperature to 32°F (0°C).
• Undisturbed ground temperaConventional Boiler/ DHW with Large Heat DHW with Small Heat
ture: 53°F (11.7°C);
Chiller and Gas DHW Pump/Small Storage
Pump/Large Storage
• Average thermal conductivity:
Heat Pumps/
1.40 Btu/h·ft·°F (2.42 W/([m·K]);
$183,000
$229,000
$210,000
Distribution
• Average thermal diffusivity:
0.96 ft2/day (0.089 m2/day);
DHW Storage Tanks
$2,400
$1,200
$7,200
• GHX was modeled to operCooling Tower
$44,000
–
–
ate at a minimum temperature of
32°F (0°C); and
GHX
–
$118,200
$97,500
• GHX was modeled to operSystem Cost
$229,400
$348,400
$314,700
ate at a maximum temperature of
85°F (29.4°C).
Cost Difference
–
$119,000
$85,300
From Conventional
Adding DHW load to the system helps balance energy loads to
Predicted Energy Cost
$17,922
$12,344
$11,256
and from the GHX, changing it
Energy Cost Savings
–
$6,344
$7,365
from cooling to heating dominant
when a DHW system with small
Simple Payback
–
18.8 Years
11.6 Years
storage capacity is used. However,
there is much greater impact when Table 4: Summary of capital cost to install conventional HVAC system compared to GCHP
the peak heat pump capacity used and GCHP integrated with hot water storage. The following assumptions were used: Cost of
to produce DHW is reduced and mechanical system estimated, cost of GHX: $15/ft ($52/m); cost of gas: $1.13/ccf ($0.40/
combined with more storage ca- m3 or $10.65/GJ); cost of electricity: $0.06/kWh with demand charge $8.00/kW. (Note:
pacity.
construction costs, GHX costs and utility rates vary significantly from one area to another
Designing a DHW system to and because of design details and equipment selection, may not represent costs in your
minimize heat pump capacity and area. These variations along with possible incentives available in your area can have an
maximize hot water storage re- impact on financial models.)
duces total borehole length in this
project by almost 1,300 ft (396 m), or 17.5%. Typical drilling climates such as the northern United States and Canada.
costs range from $12 to $22/ft ($40 to $72/m). Reducing the Cooling loads in these buildings are often driven by ocsize of the GHX improves the return on investment for the cupancy schedules rather than weather and are intermittent
owner.
and predictable.2
There may also be an impact on the energy cost, depending
In an office building cooling loads are low overnight
on the electric utility rate structure. If the utility charges “time when the building is empty, lights and computers are shut
of use” rates, or has a demand charge, there can be a signifi- down and solar gains are absent. Loads increase when
cant reduction in energy cost using TES. Reduced construc- people arrive, lights and office equipment are activated and
tion cost and possibly lower energy cost demand reduction for ventilation systems ramp up while solar gains and outdoor
some projects reduces the simple payback by seven years in air temperature increase. They drop off as people leave in
this example, as summarized in Table 4.
the afternoon. Other types of buildings, such as retail spaces or schools have their own schedules but are also fairly
Peak Building Cooling Loads
predictable.
Large buildings with large interior/core spaces often
Cooling systems are designed to meet design day loads; a
have higher peak cooling loads than heating, even in cold condition that occurs only a few hours per year. Otherwise, it
16

ASHRAE Journal

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April 2013



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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