[Equest-users] Why Water Source Heat Pump is not considered as Renewable Energy in LEED rating system?
DEldridge at grummanbutkus.com
Tue Dec 30 12:33:36 PST 2014
In the United States geothermal heat pumps - I'll refer it to them as "ground-coupled" here, a.k.a. geo-exchange, ground source - are specifically identified as a design strategy that is considered to be renewable energy for tax incentives in some cases. That's a specific designation in order to incentivize use of this type of system due to the extra construction cost.
When you take off your accounting hat and put your engineering hat back on...use of that type of ground-coupled system does displace cooling tower fans or other condensing unit energy by using the ground...so perhaps some percentage renewable. There is an added benefit for heat recovery if the system uses multiple heat pump units and some are in heating while others are in cooling. I don't think this affects the designation as "renewable" though, but does distinguish the system from air-cooled units.
However, there isn't an energy conversion process taking place in the ground. Think of it this way - energy is not extracted from the ground, it is stored and withdrawn. If the energy was only stored, there is potential for the ground temperature to increase over time. There might be properties of the ground and/or ground water that carry the excess heat away. This might be equated to using lake or river water in a chiller condenser, is that renewable? Your answer might depend on the impact to the river or lake. Similarly, installing phase change materials in your wall...high efficiency yes, but renewable...no. It's more of an issue of energy storage than energy sources.
Wind energy, solar, tidal, deep water cooling, landfill gas, and of course true geothermal heat - are a distinctly different category than ground-coupled heat pumps, and the effect of harvesting from these sources would generally be seen as negligible to the environment. This isn't true for ground-coupled systems in some cases. The GCHP system still needs to draw power from another source to run the compressors and pumps, and the use of GCHP may have varying levels of impact on the ground.
Anyway, to anser the original question about LEED - the efficiency of the ground-coupled system is modeled in EAC1 as an efficinecy measure. It would be difficult to separate a renewable component of the GCHP system energy use from those that are conventional (but high efficiency). If you compared the GCHP system to a water-loop heat pump system (with boiler and cooling tower) and showed the net savings separately from the LEED baseline, that might show the magnitude of potential "renewable" benfit from using the ground heat exchanger compared to an above-ground water loop heat pump.
In LEED the renewable energy credits have a specific purpose of reducing fossil fuel consumption. If the local electric grid is supplied from relatively clean sources, then the use of the GCHP may reduce total emissions compared to a natural gas furnce. GCHP would almost always come out ahead versus air-to-air heat pumps, electric resistance heat, or fuel oil combustion. Then similarly for cooling the efficiency of the baseline system would need to be considered. Most likely the result would be favorable against air-cooled systems, but savings may be less (or a loss) when compared against a high-efficiency water-cooled system. Then the combination of heating, cooling, and heat recovery benefit must be considered in total. Very complicated to allocate points for a GCHP compared to the other renewable energy sources that are all more or less 1:1 displacements of fossil fuel versus the baseline.
So to make a long story short, the opinion of the other posters that GCHP isn't technically a renewable energy source when used by itself and is more accurately described as an energy and cost efficiency measure seems to be supported. LEED specifically excludes GCHP as a renewable source. GCHP may qualify for financial incentive that is grouped with renewable energy sources such as solar or wind...and the whole scenario would be a lot clearer if the public didn't refer to them as "geothermal" heat pumps but instead called them ground-coupled heat pumps.
David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Direct: (847) 316-9224 | Mobile: (773) 490-5038
Grumman/Butkus Associates | 820 Davis Street, Suite 300 | Evanston, IL 60201
Energy Efficiency Consultants and Sustainable Design Engineers
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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nathan Miller
Sent: Tuesday, December 30, 2014 7:16 AM
To: YangMo; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Why Water Source Heat Pump is not considered as Renewable Energy in LEED rating system?
I would suggest that a ground-source heat pump is not fundamentally any different than an air-source heat pump (you could just as easily say a traditional heat pump extracts free heat from the air). Both use electricity to run compressors/refrigeration cycles to accept or reject heat to the ambient environment. It just so happens that ground-source heat pumps utilize a heat sink/source that is much more moderate in temperature year-round and thus realize higher efficiencies. At least in my mind that makes the GSHP a high-efficiency options, and certainly commendable, but not inherently renewable energy.
That is my best guess at the rationale. It certainly gets a bit fuzzy, especially if you start talking about taking advantage of true geothermal energy (that is high-temperature geologic features, not just stable ground temps).
Nathan Miller, PE, LEED AP BD+C - Mechanical Engineer/Senior Energy Analyst
RUSHING | D 206-788-4577 | O 206-285-7100
From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of YangMo
Sent: Monday, December 29, 2014 10:15 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Why Water Source Heat Pump is not considered as Renewable Energy in LEED rating system?
This question is not about eQUEST, but since in this group a lot of people are working for LEED consultant projects, I think it is a good place to ask this question. I have been working in U.S. for a lot of years and just came back to China recently. In China ground source heat pump and water source heat pump systems are very very popular, and they are considered as renewable energy, since they use free heat from the soil and water. But in LEED rating system, heat pump is not considered as renewable energy. Why? Is it because those system has side effect to the environment?
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