Ground-Source Heat Pumps Don’t Save Energy

GSHP- costs low now, energy saved soon
by Robert Alf

Henry has excellent points that few think about. This merely points out however that no single option necessarily makes sense without detailed analysis and comparing to other options. I would claim that GHSP make sense for at least some of my clients in MN. The following can be added to Henry's points to give a full picture for at least one of my clients:
* The source fuel for our electricity in MN is NOT 100% fossil fuel so the efficiency rating is likely higher than 31%. We have (sadly in my view) a large % of nuclear in addition to coal so let's say our efficiency is closer to 40%-45%
* Detailed usage analysis for my client shows a $1200-$1500 year savings in energy costs ... yes that is partly due to rate cuts by the electric utility so after Federal Tax Credits, this client has a rough payback of 5-7 years and will never run out of propane fuel again (very frustrating in our COLD climate)
* This client plans to install solar PV to generate much of their electricity within 5 or so years. The GSHP and related Tax Credits will help make this happen sooner

Overall, this means that for some clients, a GSHP paired with PV is a very powerful and sustainable option both from an energy and financial perspective. Since PV has a relatively long payback in our region, this pairing with GSHP helps to jump that hurdle.

not apples to to apples
by Tristan Roberts

Henry, I agree that electricity from the grid is 31% efficient, on average, and that should be factored into evaluations of GSHPs. However, you don't seem to give fuel oil burned on site the same treatment. You assume that sealed-combustion boilers burn that fuel at 92% efficiency, but what about the energy used to deliver the fuel? Can you give us an apples-to-apples comparison?

Demand Reduction
by Jeff White

Henry has a great point.
"Remember, it’s always better to reduce the amount of energy a building requires than to look for a new source of energy."

I tell my clients demand reduction is the best and number one priority. I often see demand reduction as never making it on their list. We provide super insulated thermal envelopes and can reduce the demand of a given home or building by 50% to 70% as common practice. This gain comes from our process alone. If we pay extra attention to windows and doors we can further reduce the demand. Everyone should be heads down focused on demand reduction.

It literally drives me crazy to see smart people install R13 batts or recycled news print into their walls and ceilings and then spend large sums of money on solar or GSHP systems. We all know traditional insulation systems are not sustainable over time. Even the newer homes we test (5 years old) are generally energy pigs and folks are not comfortable. This is easily solved with super insulated homes. Remember, super insulated homes are more energy efficient and more comfortable than a new source of energy.

A limited perspective?
by James Morgan

Henry's perspective on ground-source heat pumps makes a certain amount of sense if you a) look only at the heating cycle, b) assume the electricity is fossil-fuel generated and c) compare only to the efficiency of fossil-fueled boilers. Not unreasonable assumptions I suppose for a NYC resident. In other parts of the country though, one or more of those parameters might vary substantially. Here in central North Carolina for example we have a/c comprising as much or more of our residential energy usage as the heating cycle. And while air-source heat pumps are the most common installation here for both heating and cooling, and while these are even less energy-efficient than the ground-source variety, Jeff makes the better point. Load reduction by focussing on better-insulated (and smaller) homes makes much better economic and environmental sense in almost any location than fretting marginal differences in source efficiency.

I'd add that as neither natural gas nor heating oil will be available for ever and, pace bio-fuels enthusiasts, scalable carbon-neutral alternatives for those fuels are not even on the horizon, it's hard to make a case for fossil-fuel point of use heating as a long-term sustainable solution.

Meanwhile renewable non-carbon sources for electricity are gaining ground fast ...

Where is the engineering??
by Brian Haugk, MS, PE

COP is a measure of the number of units of heating obtained for each unit of electricity consumed by the heat pump. We can work out the COP at which it makes economic and environmental sense to use a heat pump (the break even point) in order to reduce carbon emissions and heating costs. At break-even point the CO2 emissions per kWh unit of gas (0.193 kg / kWh) divided by the efficiency of the condensing boiler will be equal to the CO2 emissions per kWh unit of electricity (0.432 kg / kWh) divided by the efficiency (COP) of the heat pump. Therefore, the break-even point for emissions (assuming a 90% efficient condensing boiler) is:

0.90 * (0.432 / 0.193) = 2.24 COP

Therefore, if a ground-source heat pump has a COP greater than 2.24, it will release less carbon emissions than a condensing boiler and have a higher heating output. Enclosed a chart from Department of Ecology understanding that each utility is different based on where the heat source is coming from and has a different kg/kWwh. I agree that pump energy is not included, but this effect is very small compared to the heat pump itself. Most ground source systems are in the 4.0 COP range for heating if designed properly. Cooling as noted above needs to be considered as well as the cooling from a split system used in conjunction with a furnance is normally in the 12 SEER range where a ground source is in the 20+ SEER range.

A simple comparison in WA state where energy costs are still quite low, but the comparison between gas and electric is similar:

Unit MMBtu/Unit Lb CO2/MMBtu Cost/Unit
Electricity kWh 0.003413 322 $0.075 (0.063)
Natural Gas Therm 0.1 117.08 $1.100 (0.87)

Below is a comparison of a condensing boiler, ground source heat pump, and (a third option) an air cooled heat pump producing 1,000,000 Btu of heating. All three are assumed to be producing low temperature heating water (so, for a radiant system).

Heating Technology (COP) lbs CO2 per MMBtu Heating Oprtng $ per MMBtu kWh per MMBtu Hting
Condensing Boiler 0.95 123.24 $11.58 308.42
Ground Source HP 3.2 100.63 $6.87 91.56
Air-Cooled HP 2.3 140.00 $9.55 127.39

The seaonal efficiency of the Ground Source Heat Pump accounts for ground loop pumping but is probably low at 3.2.

Conclusions:
1. Ground source heat pump is better from the standpoint of equivalent carbon production.
2. Ground source heat pump is 40% lower in terms of operating costs.
3. Energy used by the ground source heat pump requires less than 1/3 comparitively.

COP is not the whole story,
by John Howland

Henry,
Great Post,
I attended your session at the ACI Conference on Tall stuff, Tall Matters; Elevators, Pumps, Ventilation, and More. It was by far the best session that I attend that week.

12 years ago our Electric COOP said they would give me a reduce rate on my electric to change out our 80% gas forced air furnace and put in a air to air heat pump. So they set a separate meter and hook up the heat pump compressor, as the installer started to leave and I said how about the air handler blower fan motor that will run a lot longer now? He said "no that is on your regular metered rate", not such a great savings after all was said and done. Many verbal at play and even more profit driven motives. I am not saying that Heat pump are a bad Idea, just get all of the facts before you take a vacation with your project savings.

Some of the best ways to save energy don't have a box or sales person.

John

Moo!
by Steve

Jeez Henry, you'll soon be able to upholster your entire living room set in leather with all the sacred cows you're slaughtering.

Seriously tho' thank you for the sober and well reasoned look at ground-source heat pumps. I've noticed you are getting a decent amount of criticism from the other comments, but for me I'm just happy to see lively and active discussion. It really grinds my gears when an idea or a technology is presented as being above reproach and therefore discussion, or even scholarly debate. I'm really glad you brought both this and the questionable use of underfloor heating in new construction to my attention.

Re. Moo
by Anonymous

A big thank you to Brian Haugk for actually countering a not-totally-accurate article with an indepth review. It's nice to see actual numbers and evidence being brought together, and we're the better off for it.

The author makes a number of leaps of logic and faith, about the electricity source and efficiencies. He also disregards the full picture for alternatives. All that while making some good points, that we should compare systems based on primary energy usage per square foot, and implying that a lifecycle look is the proper look. The author did omit to mention that the 20+ year life of the average heat pump is two 10 or so year lifetimes for a gas furnace. But why get in to that....

Pumps, shmumps!
by Leon Kowalski

That 1999 data is gettin' kinda long in tooth, dontcha think?

The current crop of geo heat pumps typically have ECM blowers and
(ISO/ARI 13256-1) COP ratings in the 4.7 - 5.1 range for low speed
operation, and in the low 4's for full speed operation -- with an entry
water temperature of 32F (as required by ISO/ARI).

RE: pumps: The typical closed loop geo circ pump is responsible
for an 8% to 12% increase in power consumption -- and the same
reduction in COP. ...8% to 12%. Pumps, shmumps!

...BTW, how's that natural gas air conditioner workin' out for ya?

LK

geothermal
by bgsr

hmm a kwh in ny is 19 cents or 1.90 for 34,500 btu or 5.70 for 103,000 btu "100%" effecient
oil 2.89 for 137,000 btu at 86% effecient - 117,800 btu
since geo(cop of hydron is 4.3 but i'll use 3.0) is with well factored in has an kwh cost of 6 cents a kwh or 60 cents for 34,500 btu or $1.80 for 103,000 btu
what most people forget is the "mickey mouse" installing contractor who cant spell manual "j"
a truly engineered by a cureently trained contractor system makes all the difference - a poor natural gas system installed by the "seat of our pants". cant beat oil, or even air cooled heat pumps ---- i liken geo systems to the energy management "phase " all contractors went through. i waqs working on water cooled (geothermal) systems in the 60's till the water crisis - hmmmmm where did we get the current deluge of water ....

I'm just a student taking
by Jason Acosta

I'm just a student taking thermodynamics, but I came up with some different calculations for the cost of running a GSHP with a COP of 3.0 versus a 95% efficient furnace/boiler burning natural gas. Below I calculated how much it cost to produce 100,000 BTU of heat with each option. Cost of electricity is $.107 per kWh and cost of a therm is $.79 These are Colorado's average prices.

Please correct me if I'm wrong!

Furnace/Boiler- 100,000BTU/ input required=95%. Input required =105,263 BTU. 105,263BTU=1.05 therms. 1.05 therms cost $.8295

GSHP-100,000BTU/required input=3COP. 33,333 BTU input required. 33,333BTU/(3413 BTU/kWh)=9.77kWh. 9.77 kWh costs $1.05.

Looks like its still cheaper to burn gas to me. Of course this doesn't capture the whole picture and GSHPs make a net zero home possible in cold climates if you can produce enough power onsite.

Gifford is a blind moron!
by Ted Clifton

To start with, the average efficiency of a new natural-gas fired power plant is closer to 60%, not 31%. Since we are talking mostly about new construction, we need to compare new sources of energy, not antique systems serving existing homes. The average transmission line loss in the US is about 6.5%, so the net energy delivered to the house is about 56.1% efficient. Even the least efficient Ground Source Heat Pump is closer to 400% efficient, even with the water pumps included, so the GSHP is about 224% efficient with its use of natural gas. You can't even get close to that with a furnace or boiler.
Secondly, we should only be using natural gas as a way to generate electricity as a temporary means of getting past the current shortage of environmentally friendly means of generating energy. A heat pump, in itself, does not contribute to global warming, it simply moves heat from one place to another. As soon as we are able to generate all the power we need from other means, natural gas should be reserved as a mobile power source, and not squandered on providing heat and power to homes. We will too soon need all the natural gas we can find to power cars, trucks, and airplanes.

Response to Ted Clifton
by Martin Holladay, GBA Advisor

Ted,
1. Please refrain from derogatory personal comments aimed at bloggers or people who post at GBA. If you continue to use derogatory language, GBA will need to remove or edit your posts.

2. You are mistaken about the COP of residential ground-source heat pump systems. The best data on these systems were published in an article published in the April 2008 issue of Energy Design Update.

Monitoring of a system in Connecticut showed that the system COP of a house was 3.5. This was for a Water Furnace GSHP that was touted by the manufacturer as having a COP of 5.0.

Data from three houses in Vermont showed average system COPs of 2.75 for three different GSHP systems. The average COPs of the installed GSPHs, according to the manufacturers, was 4.0.

The reason that monitored COPs are always less than advertised COPs is that manufacturers EXCLUDE pumping energy from their laboratory COP measurements.

electricity
by Harry Applin

The original debate was the electrical costs on a GSHP. The amount of electricity to run a air forced system or a hydronic system is not much different than a GSHP. The big difference is that all other systems use another energy form to heat and cool. Thus, the real difference. Now adapt a solar water system and solar panels and the whole thing is off-line. No heating and cooling costs even when prices rise. No CO2. Of course, a well insulated house and new vacuum seal windows and the system would reach those COP 5

Response to Harry Applin
by Martin Holladay, GBA Advisor

Harry,
1. You suggest using a solar water system and solar panels (solar thermal panels? PV modules? hard to tell) for an "off-line" house. Is that the same as an off-grid house?

Neither a solar thermal system nor PV modules do a good job of satisfying space heating requirements for an off-grid house -- because there isn't much sun when you need it most, and because batteries can't store electrical energy for very long.

2. Those who have measured the system COP of ground-source heat pumps have never been able to measure a system with a COP as high as 5. COPs of 2.75 to 3.5 are much more realistic.

What about air-source heat pumps
by Dirk - BPI certified

Why is the talk just about "ground-source" heat pumps. Air source heat pumps are showing up in quantity for heating domestic hot water (what my wife calls Cold Water Heaters -- I confess, I think she's right; we don't heat hot water.) I digress. Digging these long holes like a mole run amok seems like a lot of work and entertains other problems. I am in Maine and I think I can see reasonable savings over fossil fueled heaters. But for people in sunny California, putting one in a garage (as they often do) seems like a no-brainer, eh? I have a family member in Fresno and he suffers temps in the 100's in his garage during the day which last well into the evening. Shouldn't be too hard to squeeze out some really hot water in that situation, no?

Hello, Thank you for
by Anonymous

Hello,

Thank you for providing this forum.

I just wanted to add some points and ask some questions.
I recently took over a house that has a ground source closed vertical loop system. The house and GSH system was built in 1990, and at that time it was, I guess, ahead of its time. The house is large, and has several heat exchanger units. Some of them are starting to fail now at 20 years. The units were made by Command Air. I gather they have gone out of business. Any idea where one can get parts? Is it worth replacing compressors?
I was advised to replace some of the units. Who makes the best units?
I did speak with a representattive from WaterFurnace, and they advised me that they expect a life cycle of 12 to 16 years on their units. I am under the impression that conventional gas furnaces can last much longer than that. Am I mistaken in that assumption?
I am wondering if these systems do require a lot more maintenance and repair due to their complexity. This does not change the energy balance discussion, but it does impact the financial calculations. I was tempted to have the system replaced by gas furnaces, and live without AC.
As they say in the tech field, "there is a leading and a bleeding edge", I am just not sure which one I am on.

Response to Anonymous
by Martin Holladay, GBA Advisor

Anonymous,
You have raised an excellent point: "I am wondering if these systems do require a lot more maintenance and repair due to their complexity. This does not change the energy balance discussion, but it does impact the financial calculations."

DX systems
by bob coleman

do the DX geothermal systems include the pumping electricity in their official COP numbers?
it seems like they would have too, which means the DX systems might run as advertised

Response to Bob Coleman
by Martin Holladay, GBA Advisor

Bob,
According to the people I trust who have measured COP (Marc Rosenbaum and Andy Shapiro), manufacturers' numbers are unreliable.

I wouldn't believe any manufacturer's numbers unless they were verified by an independent third party.

DX numbers, verified?
by bob coleman

Martin, i was sort of assuming using ASHRI(sp?) spec numbers when taking their ratings

I guess my question was, do the industry tests factor in the pumping power usage on DX geothermal systems? It is hard to read their testing spec documents to know for sure. It seems pumping the refrigerant through the ground tubes is tightly integrated into the system so i'm not sure how they'd exclude it, like the water based systems exclude the water pump which is normally external to the main system.

it seems the DX system ratings might deliver roughly as promised with the all-in-one boxes after you adjust the numbers in regard to your home compared to the standard model the testing uses

on a side note, the air source heat pumps manufacturers are not much more honest considering heating requirements, all using 45degree outside temps in the published numbers. the appliances, bodies, and dog in my house can keep things warm enough at that outside temp with no assistance ;)

Response to Bob Coleman
by Martin Holladay, GBA Advisor

Bob,
I don't know for sure about the DX pumping energy question, but I agree with your analysis. It would be hard to exclude the pumping energy required for the refrigerant cycle, so I assume that energy is included in published COP numbers.

As far as I know, all of the air-source heat pump manufacturers will provide COP specs at a variety of outdoor temperatures. I know that the Mitsubishi Web site provides COPs down to -5°F, and perhaps -13°F.

mits site
by bob coleman

yeah i saw mits posted COP numbers for those 3 mr slim models, but none of the others

using a dept of energy tool, the high HSPF for those models drops around 2.5 points which easily pushes COP numbers down towards 2. i'm assuming some of the extra features like air filtration are included in those costs which is nice if you want it.

geothermal also has that 'free' hot water
i guess the japanese use the instant hot water heaters, so mits and others don't add waste heat capturing abilities

thx again for your insight