ASHRAE Journal - April 2012 - 72

emerging technologies

residential gshPs
G
By Alissa cooperman; John Dieckmann, Member ASHRAE; and James Brodrick, Ph.D., Member ASHRAE

Efficiency With Short Payback Periods

round source heat pumps (GSHPs, also called geothermal heat pumps) provide an alternative to more conventional HVAC

systems for residential and commercial buildings. In this article, we will explore residential GSHPs. In 2010, residential buildings consumed 22.05 quads of primary energy (26.5% was consumed by space heating and 15.8% by space cooling).1 According to the 2009 Residential

Energy Consumption Survey (RECS), space heating is provided by three main energy sources: natural gas, electricity, and fuel oil.
Table 1 gives the distribution of these energy sources across the U.S. Table 2 provides a breakdown by U.S. census regions. Natural gas and electricity are the top two fuel sources. Of the homes using electricity, a little over 25% use air-source heat pumps, and the majority of these users are concentrated in the South. Similarly, out of all of the homes with air conditioning, the majority are in the South and the majority of heat pump users are also found in the South.2 Ground source heat pumps are not a new technology. They have been in use since the 1970s. However, GSHP units continue to increase in efficiency due to advances in HVAC system components. A GSHP operates by using the earth for the external reservoir, rejecting heat to the earth in the cooling mode, and taking heat from the earth in the heating mode. Around 47% of the Sun’s heat energy is absorbed by the ground. Unlike the fluctuations seen in the air temperature, the earth, below a certain depth (greater than 6 ft [1.8 m], typically, with stable temperatures after 30 ft [9 m]), remains at a constant temperature. On average, the temperature below 30 ft (9 m) is 55°F (13°C) in the U.S. This temperature varies regionally, generally being a few degrees cooler in the north and a few degrees warmer in the South.3 The energy savings of GSHPs are primarily attributable to the stability and moderation of the ground temperature. In the heating mode, a water glycol mixture circulating in the ground loop absorbs heat from the ground. It then transfers this heat to the heat pump’s refrigerant loop, vaporizing refrigerant, which is subsequently compressed, increasing its temperature and its ability to transfer heat to the home. For cooling, the process is reversed.
ashrae.org

overview of technology
A GSHP is comprised of three main elements: the ground loop heat exchanger, the refrigerant loop (heat pump), and the air-handling unit (AHU) or the heat exchanger between the refrigerant and the heating system supply water. Hydronic GSHP configurations use the latter configuration.3
72 ASHRAE Journal

Overall, one unit of energy from the grid is converted into 4 – 6 units of heating or cooling energy output; about 3 – 5 units of energy are supplied from the ground.3 There are two halves to a GSHP, the underground heat transfer loop and the above-ground heat transfer system and HVAC components. The above-ground components are the same as those found in conventional HVAC systems. Advancements made in compressor, AHU, and motor drive technology have been carried over to the GSHP. The key and unique technology to the GSHP is its ground loop. This loop can be configured as open or closed. Closed-loop systems can be configured either vertically or horizontally.3,4 Open-loop systems are the oldest type. They account for at most 20% of the US market. Groundwater is the ground source heat carrier. It directly enters the groundwater heat exchanger of the heat pump and after transferring heat to or from the working fluid is discharged to a well or surface body of water. This type of loop requires proximity to a supply of pure ground water. Open-loop systems are sometimes prohibited due to municipal regulations protecting groundwater. Closed-loop systems circulate water or a water glycol mixture through a buried heat exchanger loop in contact with the earth. Vertical loops or boreholes require holes up to 300 ft (91 m) deep per ton of capacity required. This can add up to 600 ft (183 m) of piping. Multiples of these loops can be arranged in either series or parallel. Series loops require larger piping and are limApril 2012



ASHRAE Journal - April 2012

Table of Contents for the Digital Edition of ASHRAE Journal - April 2012

ASHRAE Journal - April 2012
Contents
Commentary
Industry News
Meetings and Shows
Letters
Feature Articles
Effects of Typical Inlet Conditions on Air Outlet Performance
Designing for IAQ in Natatoriums
Shielding Fresh Air Ventilation Intakes
Don’t Turn Active Beams Into Expensive Diffusers
Technology Award Case Studies:
Deere: Running Efficient
Standing Columns
Building Sciences
Washington Report
Emerging Technologies
Refrigeration Applications
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2012 - ASHRAE Journal - April 2012
ASHRAE Journal - April 2012 - Cover2
ASHRAE Journal - April 2012 - 1
ASHRAE Journal - April 2012 - 2
ASHRAE Journal - April 2012 - Contents
ASHRAE Journal - April 2012 - Commentary
ASHRAE Journal - April 2012 - 5
ASHRAE Journal - April 2012 - Industry News
ASHRAE Journal - April 2012 - 7
ASHRAE Journal - April 2012 - 8
ASHRAE Journal - April 2012 - 9
ASHRAE Journal - April 2012 - 10
ASHRAE Journal - April 2012 - 11
ASHRAE Journal - April 2012 - 12
ASHRAE Journal - April 2012 - Letters
ASHRAE Journal - April 2012 - Meetings and Shows
ASHRAE Journal - April 2012 - 15
ASHRAE Journal - April 2012 - Effects of Typical Inlet Conditions on Air Outlet Performance
ASHRAE Journal - April 2012 - 17
ASHRAE Journal - April 2012 - 18
ASHRAE Journal - April 2012 - 19
ASHRAE Journal - April 2012 - 20
ASHRAE Journal - April 2012 - 21
ASHRAE Journal - April 2012 - 22
ASHRAE Journal - April 2012 - 23
ASHRAE Journal - April 2012 - Designing for IAQ in Natatoriums
ASHRAE Journal - April 2012 - 25
ASHRAE Journal - April 2012 - 26
ASHRAE Journal - April 2012 - 27
ASHRAE Journal - April 2012 - 28
ASHRAE Journal - April 2012 - 29
ASHRAE Journal - April 2012 - 30
ASHRAE Journal - April 2012 - 31
ASHRAE Journal - April 2012 - 32
ASHRAE Journal - April 2012 - 33
ASHRAE Journal - April 2012 - Shielding Fresh Air Ventilation Intakes
ASHRAE Journal - April 2012 - 35
ASHRAE Journal - April 2012 - 36
ASHRAE Journal - April 2012 - 37
ASHRAE Journal - April 2012 - 38
ASHRAE Journal - April 2012 - 39
ASHRAE Journal - April 2012 - 40
ASHRAE Journal - April 2012 - 41
ASHRAE Journal - April 2012 - 42
ASHRAE Journal - April 2012 - 43
ASHRAE Journal - April 2012 - Deere: Running Efficient
ASHRAE Journal - April 2012 - 45
ASHRAE Journal - April 2012 - 46
ASHRAE Journal - April 2012 - 47
ASHRAE Journal - April 2012 - 48
ASHRAE Journal - April 2012 - 49
ASHRAE Journal - April 2012 - 50
ASHRAE Journal - April 2012 - 51
ASHRAE Journal - April 2012 - Don’t Turn Active Beams Into Expensive Diffusers
ASHRAE Journal - April 2012 - 53
ASHRAE Journal - April 2012 - 54
ASHRAE Journal - April 2012 - 55
ASHRAE Journal - April 2012 - 56
ASHRAE Journal - April 2012 - 57
ASHRAE Journal - April 2012 - 58
ASHRAE Journal - April 2012 - 59
ASHRAE Journal - April 2012 - 60
ASHRAE Journal - April 2012 - 61
ASHRAE Journal - April 2012 - Building Sciences
ASHRAE Journal - April 2012 - 63
ASHRAE Journal - April 2012 - 64
ASHRAE Journal - April 2012 - 65
ASHRAE Journal - April 2012 - 66
ASHRAE Journal - April 2012 - 67
ASHRAE Journal - April 2012 - 68
ASHRAE Journal - April 2012 - 69
ASHRAE Journal - April 2012 - Washington Report
ASHRAE Journal - April 2012 - 71
ASHRAE Journal - April 2012 - Emerging Technologies
ASHRAE Journal - April 2012 - 73
ASHRAE Journal - April 2012 - 74
ASHRAE Journal - April 2012 - 75
ASHRAE Journal - April 2012 - 76
ASHRAE Journal - April 2012 - 77
ASHRAE Journal - April 2012 - 78
ASHRAE Journal - April 2012 - 79
ASHRAE Journal - April 2012 - 80
ASHRAE Journal - April 2012 - Refrigeration Applications
ASHRAE Journal - April 2012 - 82
ASHRAE Journal - April 2012 - 83
ASHRAE Journal - April 2012 - Products
ASHRAE Journal - April 2012 - 85
ASHRAE Journal - April 2012 - Classified Advertising
ASHRAE Journal - April 2012 - 87
ASHRAE Journal - April 2012 - Advertisers Index
ASHRAE Journal - April 2012 - Cover3
ASHRAE Journal - April 2012 - Cover4
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