Ground source heat pump feasibility

1915_foursquare

Thanks to everyone who responded on my mini split questions.

I have been told to take a second look at ground source but am not sure what the main considerations are in my situation.  

We have a 1600 sq ft Foursquare, built 1915 with as much cellulose as we could get in it, located in Western Massachusetts.  Current heat is a WM97+ gas boiler, cast iron baseboard radiators, and a hydronic floor in one bathroom.  Current cooling is window AC.

if we did (closed loop vertical) ground source, would water to water work with our existing radiators or are they undersized?  When I looked at air source air to water that was a concern due to much lower operating temperatures for the air to water; is water to water higher temperature?

Would cooling be a fan coil system or would we have to put in ducts?  We don’t have ducts now or much space for them.

Thanks!

Hot_water_fan

It’s the same deal as air source. You’ll have a water temperature issue most likely, dealt with the same ways as air source. Ground source is much more expensive, that’s the main hurdle for your situation - as houses get smaller ground source gets worse and worse. 

1915_foursquare

Hot_water_fan said:

It’s the same deal as air source. You’ll have a water temperature issue most likely, dealt with the same ways as air source. Ground source is much more expensive, that’s the main hurdle for your situation - as houses get smaller ground source gets worse and worse. 

Why does ground source get worse for smaller houses?  Is it that the installation costs don’t scale linearly with house size due to the drilling cost not varying much?

Hot_water_fan

Why does ground source get worse for smaller houses?  Is it that the installation costs don’t scale linearly with house size due to the drilling cost not varying much?

Bingo: you need to spread the costs over many, many BTUs to come close to air source. It’s great for large campuses. Houses, less so. 

ethicalpaul

Or you need to live there for some time. The COP never really changes and it can and will supply the same heating/cooling all year around, even where Jamie lives. It's just so much better than air source.

Jamie Hall

Agree with both @Hot_water_fan and @ethicalpaul . Grond source heat pumps work, and work well, in pretty much any climate. They do not -- so far at least -- produce really hot water, so the radiation in older establishments may be inadequate -- but don't overlook using them to power air handlers instead, if you have adequate ducting.

The down side to them is installation. If you are in a warm enough climate that the source -- ground -- side can be a relatively shallow (say less than 6 feet to avoid trenching problems) shallow grid, they aren't too bad -- although a lot more expensive than air source! -- provided you have the land area, and the cost will scale with size at least to an extent. If you are in a colder area or dealing with a restricted area or shallow to bedrock, and you have to go with deep well source arrangements, the cost really doesn't scale -- drilling a hole in the ground just plain costs money. Much money. And the amount of much doesn't vary that much with scale.

1915_foursquare

@Jamie Hall thanks!  We are in MA on 1/8 acre so it would have to be a vertical closed loop system.  We are at the base of a hill that is a glacial remnant, and have been told the hill is basically solid rock, so that might make the drilling more challenging.  We do intend to stay in the house indefinitely.

We don’t have any ducting and it would be tight to put any in.  

Hot_water_fan

Yup, ground source is amazing for ~1 - 5% of houses. It’s got low market share but when it works, it works!

Lance

My experience with ground source heat pumps is this. 1) they are purchased if there is a significant tax break to help pay for it. 2) Those I have seen lacked the test gauges and points for test to commission and adjust flow rates properly. There is never any documentation to prove it works. Essentially, they operate as an air-to-air heat pump without the ground source BTU. It is ignored because it cannot be seen. Today I look at the latest air heat pumps and their much lower outdoor temp heat capacities. You get results for comfort. And the savings far outperforms the extra cost for ground source and the maintenance foe years to come. Consider the loads. It takes a large load to justify smaller savings. Homes heat loads are not as much as older ones were. Life cycle cost factors like repairs and maintenance and even the quality of the techs available should be considered. Just thinking, LB.

Jamie Hall

I get a bit of a chuckle out of your comment 1), @Lance . Around here the tax assessors will happily increase your real estate tax if you install a heat pump -- never mind a ground source heat pump -- and the increase is enough to wipe out any energy cost savings in short order. Go figure.

ethicalpaul

Hmm Lance I'm not sure what you mean about the lack of documentation/proof of ground source BTU, maybe I'm misunderstanding.

It's all pretty straightforward. They know how much btu they get from a certain depth in various earth conditions. I'm talking about vertical wells here, the only kind I would personally use. They use an engineered temperature-conductive grout to fill the well and it's all scientifically understood.

After installation it is super easy to see the delta-T of the ground loop, so you can use that with the flow rate to know the btu transfer very accurately.

@1915_foursquare, don't worry about the rock. I had mine drilled in CT where the granite bedrock started 20 feet below grade, as did the water. Your drill contractor knows what is under the dirt in your area and how deep.

The drill uses air pressure and some water and a hardened bit to basically pulverize the rock and flush out the resulting silt from the hole, it's quite impressive. And the sooner they hit solid rock, the less length of steel sleeve they need.

hot_rod

The heat load of the building and the type of emitters are key to hydronic heat pumps.

A NYSERDA (NY) study found that 80% of the heat season you are above design day conditions.

We did a case study on this building in NY in a -5 design climate, on our Coffee with Caleffi webinar today.
You can view the webinar on the Caleffi You Tube channel in a few days.

It was designed for a 120 SWT. It ran last year with 90 ° swt!

A design that provides heat, cooling, buffer tank and DHW or preheat.

H2OBandit603

Even as a well driller who has designed and drilled a few open and closed loop geothermal systems I always tell people to look into Air source heat pumps knowing the upfront cost on my end is going to be a massive layout of capital.  I won’t list prices because of the rules but I’ve done a few new construction, open loop, most recently two 500’ wells in Jackson NH, the white mountains, he installed a 6 ton forced air unit, pump out of the first well, dump into the second well,  a 3/4 hp constant pressure pump in one well just to run the geothermal heat pump at 30 psi, another 1.5 hp pump in the other well for his residential use at 70 psi and provisions to use either pump as backup to the other should one fail, etc and a return line from the geothermal heat pump down the residential well.  Granted it was a dual purpose project, water AND a heating source, but just our end of the project was easily double what it would have cost just for residential well.  Twice the work, twice the materials.  Also this whole system was contingent on hitting a bunch of high quality water.  We didn’t even discuss doing geothermal until the first well was complete and we knew we had a viable design.

I did own a home I installed a geothermal forced air system that I really liked, you could chill meat with the air conditioning. Duct wasn’t big enough the first time though, should have hired somebody who knew what they were doing instead of letting a plumber buddy of mine tell me what to install and “it’ll go”. It did not go I needed to redo the ductwork.  Hire a professional lol.

GW

I admit- i have become a grumpy nay-sayer when it comes to geothermal. The one topic that gets overlooked is 'what is the loop temp'. Good luck with getting that answer- it's an unknown factor unless someone does an actual 'test loop' (never seen it with my own eyes, just in the textbooks). The colder the loop, the harder the compressor works. If you're extra unlucky, your heating bills will be higher than that of a well-installed mini system. But it's clear to me that a properly installed geo is a very good thing. I have one at my home and my business, but the nat gas costs are simply lower (elec rates are very high in my area). My house--I can heat the home in single digits with no backup (just water). Most systems have anti-freeze pumped in, which means cold loop temps. Why go through the costs and the hassle if you're going to have a cold loop?