We are getting proposals for a ground source heat pump in Portland, OR and receiving some contradictory information. We initially talked with a HVAC contractor who specialized in earth coupled heating systems when doing renovations several years ago, and, after getting his recommendations on doing a horizontal closed loop system, had our building contractor dig trenches for a 400' six pipe system based on the HVAC contractor's recommendation for a 340' six pipe straight run loop with 1' between pipes (we have very limited space in our lot, short of destroying accessory structures or cutting trees). My husband rolled out the coils in the excavator's trenches, and all went pretty smoothly. The trenches are at least four feet deep and about 75% of them have been covered with an additional 2 feet of fill from our house addition basement excavation. We added another 200 l.f. of pipe by having the pipe run 2.5' deep at 3' o.c. under the addition's basement slab gravel before re-entering our house (the slab has 4" of blueboard under it) - 2,600 feet of total pipe.

After several years of continuing renovations, we finally have the money to pay for the heat pump that the HVAC contractor had proposed. All is well and good, except the system that cost $12k four years ago, now apparently will cost $18k. The contractor says the price of heat pumps has skyrocketed due to Federal efficiency improvement requirements, etc. We were a little taken aback to say the least.

We contacted another HVAC geo specialist for a second proposal and he is having problems with our pipe install design. He says that the pipe installed under our house and down the driveway could freeze the soil and cause driveway and foundation damage. This is the first we've heard of this and it was never mentioned by the first contractor. The second contractor is recommending that the largest heat pump we should install be a 2-ton system to keep it from freezing, with both a backup domestic hot water boiler and an instant hot water heater for the hydronic heating to make up the difference for the undersized heat pump. They would provide a Bosch HP with a 30 gallon tank dedicated just to the HP and use our existing 55 gallon WH. He has not written a formal proposal yet.

The first contractor is proposing NSW050 WaterFurnace four ton unit with an 80 gallon "hot water assist" water heater.

Both contractors have done a heat load calc and both are mechanical engineers. The first contractor has been doing geothermal for decades. I know this is scant information, but any feedback is appreciated.

Our specific questions are these: 1. When we contacted the first contractor years ago, he indicated that the Water Furnace model he was recommending then would cost about $7k - so 12k for his total installation costs seemed not unreasonable. Have heat pumps really almost doubled in price, or is he just taking advantage of the rush before Federal incentives expire? 2. We read about many systems where people put their geoloops under their houses - how come we have not read of frozen ground heaving as being an issue before now? 3. Did we undersize our loop? The first contractor's heating load calculations indicate a load of 39,503 BTU/HR (not sure how to read the report). And he based that calculation on standard insulation values, and our house is now super insulated with the completed portion having an ACH of 0.9 (we worked hard on making it tight).

Where has my paragraph spacing gone! Sorry about the run-on sentences. :) Alexis.

Update: Found the break symbol and inserted my own paragraph breaks.

The spacing thing is a problem with I think Internet Explorer....We see it all the time....use Chrome. Any which way....another option is buying the cheaper/small geo unit and in the loop installing a plate heat exchanger to your current domestic hot water tank. The geo unit can be stage one and then turn on a pump for the plate exchanger for stage 2. I bet down the road if the geo unit went out the plate exchanger will still keep up with the full load. This happened at my current house, worked great. The cost savings of the small unit might pay for the plate heat exchanger and pump. Also the geo unit being on the small side it won't short cycle as much and be more efficient. Good luck.

39,503 BTU/HR ... based that calculation on standard insulation values, and our house is now super insulated

Given this, 2 tons should do a good job and cover most of your heating load. Your engineer should be able to estimate how much based on previous year heating bills (or less accurately, another Manual J). Another approach would be to install a slightly larger heat pump and monitor the loop temperature or surrounding soil for freezing temps. Yet another would be to forget geo and buy a Chiltrix air source heat pump.

http://www.chiltrix.com/documents/price-list.html

Posted By newbostonconst on 18 Nov 2016 03:17 AM


...another option is buying the cheaper/small geo unit and in the loop installing a plate heat exchanger to your current domestic hot water tank. The geo unit can be stage one and then turn on a pump for the plate exchanger for stage 2.

I bet down the road if the geo unit went out the plate exchanger will still keep up with the full load.

Thanks NewBoston, I think your recommendation is what both contractors are proposing - Our hydronic system has a heat exchanger with the current 55 gallon electric hot water tank - that alone is able to keep up with the 1100 s.f. of home that is currently occupied, but 2nd showers can be kind of tepid.

Jonr, We have not occupied the improved portions of our house - mostly DIY/pay as you got the money = years of living in a construction site - so we don't know what the total heating bill will be.
On the Chiltrix heater - is their COP number to be believed? Up to 597% I understand that that number is not an average, but when you factor in the extra costs for a geothermal unit, I can see the overall cost advantages. We only have about $3200 in for the cost of piping, pressurizing fittings, and excavating (I'm the accountant in the family), so we would not lose that much on what we put in so far. We are still waiting for a proposal from the second contractor, so we'll start weighing the benefits. It was the 30% tax rebate that made the geothermal seem so enticing when we began the project. We will give your suggestion serious consideration.

I don't want to get too off topic before someone can comment on our three questions - anyone have any experience with small loop performance, ground freezing and heaving, or heat pump escalating costs?

If your house is truly "superinsulated," in that it has insulation levels way above "code," good windows (eg. triple pane), and is very tight (your 0.9 AC50 qualifies), then I have to think that the first contractor's calculation of 40KBTU/hr is way above what your house ought to see, particularly in your location. For reference, our house, built 2010-11, is in climate zone 6 (central NH), is superinsulated, and has two levels on a ground footprint of 2000 sqft. At that time, the regional distributor of CM heatpumps and two of their approved installers all reported heat loads of around 55KBTU/hr and recommended a five-ton heat pump. My own spreadsheet calculation, after the blower door test was first done (0.65 ACH50, final of 0.80), showed 22KBTU/hr. Only one of the installers was willing to provide details of their calcs. Side by side comparison with my own calcs showed that their assumptions had badly overestimated the heat load. I am convinced that a good heat load calc for a superinsulated house requires a lot of detail and time, which contractors can't or won't spend on a proposal that may not come in. Manual J calcs are known to overestimate heat loads, and for such a house no assumptions can be made.

In the end, I specified a two-ton unit, which in practice keeps the house at 70 F in just first stage, at design outside temp (-3 F for me). My best calculation of actual heat load from the hour meter during a three-day period when the outside temp swung a few degrees to either side of 0 F, is more like 19KBTU/hr.

I can't speak about your ground connection. Mine uses the standing column well (SCW), semi-open loop method. Also, for your location, I have to agree with JONR that you ought to consider an ASHP over the expense of a GSHP. But given that your ground loops are in place, then if a good, detailed heat loss calc shows that a two-ton unit will suffice, as I suspect will be the case if your house truly is superinsulated and not huge, then you may be fine going that route.

Not sure if I understand the concerns, or would suggest that some of the concerns are not really concerns.

1) It appears that your actual load numbers are lower than estimated, and you have 2400-2600 ft of pipe in the ground, between 4-6 ft deep.
2) The $$$ difference between a 2, 3 or 4 ton w-w heat pumps are minuscule.
3) The impact on the given ground loop you have, of a 4 ton heat pump satisfying 100% of the load versus 2 tons satisfying 95% of the total load, is also minuscule.
4) W-W heat pumps should be designed for full load.
5) Making the heat pump smaller and supplying it with all kinds of backup equipment only increases costs and complexity
6) You already have a heat pump there to make large amounts of hot water, why bothering with a desuperheater and hot water assist. Have the heat pump make 100% of your domestic hot water.
7) We see some ice formation around the pipes, but not enough to heave the ground up to damage parking lots etc. We always put the geo header pipes underneath the basement slab in new constructions.
8) Not knowing the local ground characteristics, but in moderate Oregon climate with moist soils, you seem to have enough pipe in the ground to support a 4 ton heat pump, especially given your low load numbers.
9) Hot Water generating ASHP do run with an average COP between 1.5 and 2.0 in your climate, at best. Do not believe their "up to" efficiency claims.

Tell us more about the house, all radiant? need for A/C?

I've seen no reason to disbelieve the Chiltrix claims below. And I certainly wouldn't use any data from other heat pumps to characterize CX30 performance.

http://www.chiltrix.com/chiller-technology.html

Just how much freezing/displacement you can tolerate before something x distance away experiences frost heave is a good question.

DickRussel, what you have written is most reassuring – we are so enjoying the radiant heat, and except for the week or so each year it gets in the high 90s or above when some would prefer AC, we can’t see why anyone wouldn’t install infloor heating – no drafts and my feet love it, especially in the bathroom. What program did you use to do your heat-calcs?

DocJenser, thanks for the thoughtful reply.

The primary concern is just understanding how there could be such dramatic differences between the two contractor’s recommendations – perhaps we are just looking for reassurance for things that are no-brainers for experienced professionals, but incomprehensible to the uninitiated – that’s why these forums are so valuable for the consumer.

Posted By docjenser on 19 Nov 2016 11:57 AM

2) The $$$ difference between a 2, 3 or 4 ton w-w heat pumps are minuscule.
3) The impact on the given ground loop you have, of a 4 ton heat pump satisfying 100% of the load versus 2 tons satisfying 95% of the total load, is also minuscule.
4) W-W heat pumps should be designed for full load.
5) Making the heat pump smaller and supplying it with all kinds of backup equipment only increases costs and complexity

So, if what you saying is that there is little relative cost difference between 2 to 4 ton units, installing a larger size unit to make more profit is not likely the motivation of the first contractor – that’s good to know. The second contractor said that the 30 gallon buffer tank was to help reduce short cycling, something mentioned often in discussions of under performing systems. After our experience with running low on hot water when taking a shower during or just after the hydronic system has run, we asked the second contractor if we should consider a 100 gallon tank (5 bedrooms with at time 10 or more children/grandchildren and relatives visiting at once – that’s when we run out of water quickly), but he said there would be little difference in the overall performance of the system and that’s where the backup heating (electric – no gas ) would most likely kick-in. This is where my understanding of such systems falls short: I understand that there is only so much heat available around our loops, and that if we extract heat continuously over a short period of time, the surrounding soils will essentially run out and will need time to allow conduction to reheat that soil. So, why not extract more of that heat ahead of time – maybe days ahead – if it sits in the tank and loses heat to the utility room, at least it’s inside the house (and our utility room is unheated and often the coldest room in the house with the HRV supply duct dumping there and on top of the refrigerator niche – vents on three sides of the utility room accommodate make up air for the distributed HRV exhaust ducts)? We even asked the contractor why not have two hot water tanks – one for the hydronics and one for domestic use, but he again said it would do nothing to make the system more efficient or perform better.

Posted By docjenser on 19 Nov 2016 11:57 AM

8) Not knowing the local ground characteristics, but in moderate Oregon climate with moist soils, you seem to have enough pipe in the ground to support a 4 ton heat pump, especially given your low load numbers.

The recommended size of the units is the most puzzling aspect of the differences between the two proposals – we have not gotten the quote or a heating load report from the second contractor yet, but we’ve emailed him and asked him if he has any personal experience with ground heaving and he has simply ignored the question to date. My hope is that there is some sort of standardization in the industry as to how to calculate the available heat for the given loop parameters, so we’ll know that it’s an apples to apples for at least their starting points for designing the system.

A side note in regards to heat load calcs – we told the first contractor that we had built the house almost exactly to plan (we increased some of the wall depths), but he did not revise his heating calculation. It was not until writing on this forum that my husband noticed this – one of the reasons we are hoping to get some feedback on average heat pump installation costs is that we suspect that he is hoping we’ll just bite the bullet and pay the upcharge without doing any more work. I hate price shopping, but I also realize that only way to know whether you are getting reasonable proposals is to get more than one estimate. Considering the slow response of the second contractor – four weeks since his initial visit – we may be getting a least a third bid.

Posted By docjenser on 19 Nov 2016 11:57 AM

Tell us more about the house, all radiant? need for A/C?

No A/C. The house is an older home that had 2x4 stud wall, no insulation, and no sub-sheathing, so we (mostly my husband) stripped the siding off and thickened out the walls with another row of studs offset from the existing and put plywood on, with the cavity being at least 7-1/2” throughout. The additions have Quadlock ICF foundations with 2” on the inside and 4” on the outside (everbody now tells us the 4” should have gone to the inside) and double 2x4 walls above. Blown-in cellulose in walls and attic. All radiant heating with 11 zones and dual sensor thermostats, staple up with metal plates under the fir floors (no subfloor sheathing – old growth CVG fir) and top of subfloor system elsewhere. My husband and I did much of the pipe installation together, though he drilled 100% of the holes. The final house size with mostly finished basement is 3100 sf with three roughly equal floors.

Posted By AlexisB on 19 Nov 2016 03:53 PM
DickRussel, what you have written is most reassuring – we are so enjoying the radiant heat, and except for the week or so each year it gets in the high 90s or above when some would prefer AC, we can’t see why anyone wouldn’t install infloor heating – no drafts and my feet love it, especially in the bathroom. What program did you use to do your heat-calcs?

I didn't use a canned program for the heat loss calcs. I built my own spreadsheet. Sure, that was more work, but it gave me total control over the calcs, with no uncertainty as to what was going on behind the scenes of a program. I had all the measurements of the house, U values for all the windows, R values for every wall section, foundation, and attic floor. Steady state heat loss due to conduction is basically simple: Q = U *Area *delta T, where Q is BTU/hr, U is heat transfer coefficient, BTU/ft2/hr/deg F, and delta T is temperature difference, from inside to outside. New windows come with stickers giving the U for the assembly. For insulated walls, U by definition is 1/R. Each part of the exterior shell has an area and a U. Also, the insulated basement slab will have its own delta T, and the insulated foundation walls will have a delta T varying with depth below grade. Losses to ground have the most uncertainty, but with enough insulation the loss will be small, so a higher uncertainty in a small rate doesn't affect the total much. For air infiltration, I had two parts. One, the house has an HRV for fresh air and winter humidity control. I assumed an 80% efficiency (mfg literature claims higher). From the operating CFM and air density and heat capacity, the hourly heat loss from air rejected through the exchanger is then 20% of the mass*heat capacity*delta T. Then I allowed for straight air leakage, by dividing the blower door test CFM50 by 18, a very crude approximation of the ratio of blower door rate to "natural" leakage rate. So I had a number for each part of the exterior shell, and the totaling is automated. I did tweak a few things during design to see the effect on the total.

One comment on radiant floor heating, particularly for a basement slab. Bare concrete doesn't feel anywhere near warm to feet without shoes on until it gets to around 78-80 F. But that is a large surface area. If a house is truly insulated, that heat has little place to go, and keeping the slab that warm would quickly raise the room temperature to a point of being uncomfortably warm. For control, the circulating water temperature would have to be low 70s, too low for that warm feet feeling. General advice for a superinsulated house is to skip the radiant floor heat, keep your slippers on, or cover the concrete with thin carpeting or laminate flooring. Put the money and effort spent on the in-floor plumbing into the exterior shell.

True, your feet won't feel warm in a super insulated house - unless you install a Chiltrix with the outdoor unit indoors :-).

Posted By DickRussell on 20 Nov 2016 01:16 PM
I didn't use a canned program for the heat loss calcs. I built my own spreadsheet...

I can see the utility of going through that kind of work when I look at the report from our first contractor - he has duct leakage loss and a host of other variables that have positive values that don't apply to our project. Did your contractor object to your lower heat-loss numbers? Seems like you might risk stepping on some toes - we definitely got some eye-rolls when we showed these two contractors our hydronic system, but when we asked if they would do anything differently, they both said the system was perfectly adequate as we have it.

Posted By DickRussell on 20 Nov 2016 01:16 PM
One comment on radiant floor heating, particularly for a basement slab. Bare concrete doesn't feel anywhere near warm to feet without shoes on until it gets to around 78-80 F...

I truly have not given it much thought, but my husband obsessed over the areas we did not distribute the pipes to after we first occupied the space - lesson learned was run pipes evenly and everywhere under a basement slab, including at least some portion of the laundry room. However, we never run heat to our bedroom until it's well below freezing (which is very rare in Portland), and it stays at a relatively constant temperature between 62 and 68, and 62 is the set point for calling heat). We keep the door closed to keep it cooler. When you walk on that floor, it does feel cold, while the rest of the house just feels cozy. The exception is the bathroom, which has it's own thermostat - I keep that very noticeably warm by dialing up the floor sensor - my husband thinks that's a waste of heat because it has the largest HRV exhaust duct going to it, so we are pulling heat from the warmest room. Although I leave the door open on purpose to further help keep the floor loops running ;).

Anyone have any input on our original cost question? I've realized I rounded the heat pump number downward and it's actually $18,900 for the HP and purging the loop pipes.

You can go here to get an idea of prices for the HP itself. IMO, installing a water-to-water HP to existing input and output lines shouldn't add much. It's not clear how much more than that you really need.

Air source heat pumps seem to be a more competitive market with better prices and technology (eg, inverters).

Posted By AlexisB on 20 Nov 2016 06:16 PM
......
I can see the utility of going through that kind of work when I look at the report from our first contractor - he has duct leakage loss and a host of other variables that have positive values that don't apply to our project. Did your contractor object to your lower heat-loss numbers? Seems like you might risk stepping on some toes.....

I sent the area distributor and two approved installers all of the details of the house construction, plus my own results. It seems they all ignored most of the detailed information. The numbers from the one contractor who provided that showed a 10,000 BTU/hr heat loss for "fireplace," when there is none, an incorrect assumption on his part. Then there was a much higher number assumed for air leakage, and some wall R values picked from  a drop-down list that were way below actual. That stuff accounted for 80% of the difference; the rest was miscellaneous, and all due to assumptions made and shortcuts taken to reduce the amount of detailed information input to the program.

The area distributor of the equipment said they would provide the two-ton unit per my request, vs the five-ton recommended unit, but also said they wouldn't stand behind the performance if it failed to keep the house warm. I had the duct work and unit installed by a local contractor not originally on the approved contractor list. I later sent the distributor actual performance information, showing that the two-ton unit kept the house warm in just first stage, but they never responded to that. It didn't bother me if I offended anyone who did the obviously incorrect heat loss calculations. I knew my numbers were right and theirs were wrong.

Posted By jonr on 19 Nov 2016 02:27 PM
I've seen no reason to disbelieve the Chiltrix claims below. And I certainly wouldn't use any data from other heat pumps to characterize CX30 performance.

http://www.chiltrix.com/chiller-technology.html

Just how much freezing/displacement you can tolerate before something x distance away experiences frost heave is a good question.

It is a rating game. Nothing to do with real world performance. And given the size and specs from the heat exchanger, and the load numbers, I would question if any freezing will occur at all.

Posted By AlexisB on 19 Nov 2016 03:53 PM
The primary concern is just understanding how there could be such dramatic differences between the two contractor’s recommendations – perhaps we are just looking for reassurance for things that are no-brainers for experienced professionals, but incomprehensible to the uninitiated


So, if what you saying is that there is little relative cost difference between 2 to 4 ton units, installing a larger size unit to make more profit is not likely the motivation of the first contractor – that’s good to know. The second contractor said that the 30 gallon buffer tank was to help reduce short cycling, something mentioned often in discussions of under performing systems. After our experience with running low on hot water when taking a shower during or just after the hydronic system has run, we asked the second contractor if we should consider a 100 gallon tank (5 bedrooms with at time 10 or more children/grandchildren and relatives visiting at once – that’s when we run out of water quickly), but he said there would be little difference in the overall performance of the system and that’s where the backup heating (electric – no gas ) would most likely kick-in. This is where my understanding of such systems falls short: I understand that there is only so much heat available around our loops, and that if we extract heat continuously over a short period of time, the surrounding soils will essentially run out and will need time to allow conduction to reheat that soil. So, why not extract more of that heat ahead of time – maybe days ahead – if it sits in the tank and loses heat to the utility room, at least it’s inside the house (and our utility room is unheated and often the coldest room in the house with the HRV supply duct dumping there and on top of the refrigerator niche – vents on three sides of the utility room accommodate make up air for the distributed HRV exhaust ducts)? We even asked the contractor why not have two hot water tanks – one for the hydronics and one for domestic use, but he again said it would do nothing to make the system more efficient or perform better.

Posted By docjenser on 19 Nov 2016 11:57 AM

8) Not knowing the local ground characteristics, but in moderate Oregon climate with moist soils, you seem to have enough pipe in the ground to support a 4 ton heat pump, especially given your low load numbers.

The recommended size of the units is the most puzzling aspect of the differences between the two proposals – we have not gotten the quote or a heating load report from the second contractor yet, but we’ve emailed him and asked him if he has any personal experience with ground heaving and he has simply ignored the question to date. My hope is that there is some sort of standardization in the industry as to how to calculate the available heat for the given loop parameters, so we’ll know that it’s an apples to apples for at least their starting points for designing the system.

A side note in regards to heat load calcs – we told the first contractor that we had built the house almost exactly to plan (we increased some of the wall depths), but he did not revise his heating calculation. It was not until writing on this forum that my husband noticed this – one of the reasons we are hoping to get some feedback on average heat pump installation costs is that we suspect that he is hoping we’ll just bite the bullet and pay the upcharge without doing any more work. I hate price shopping, but I also realize that only way to know whether you are getting reasonable proposals is to get more than one estimate. Considering the slow response of the second contractor – four weeks since his initial visit – we may be getting a least a third bid.

Posted By docjenser on 19 Nov 2016 11:57 AM

Tell us more about the house, all radiant? need for A/C?

No A/C. The house is an older home that had 2x4 stud wall, no insulation, and no sub-sheathing, so we (mostly my husband) stripped the siding off and thickened out the walls with another row of studs offset from the existing and put plywood on, with the cavity being at least 7-1/2” throughout. The additions have Quadlock ICF foundations with 2” on the inside and 4” on the outside (everbody now tells us the 4” should have gone to the inside) and double 2x4 walls above. Blown-in cellulose in walls and attic. All radiant heating with 11 zones and dual sensor thermostats, staple up with metal plates under the fir floors (no subfloor sheathing – old growth CVG fir) and top of subfloor system elsewhere. My husband and I did much of the pipe installation together, though he drilled 100% of the holes. The final house size with mostly finished basement is 3100 sf with three roughly equal floors.

You need two tanks, one for the domestic hot water, and one buffer tank for the radiant system to reduce short cycling. Again, you can skip the desuperheater part and the buffer tank for the desuperheater. Besides heating your house, you need extra capacity for your domestic hot water, and also to heat up the floors before you start heating the space, which we call thermal inertia. Thus you will need higher peak capacity from your heat pump than what your manual J tells you. So lets say you have a cold night and need about 25,000 BTUs/h to heat your super insulated 3100 sqf house, but also you need to heat up the floors in addition, lets say with 7000 extra btus/hour. Then you fill some bathtubs, and now you need 5000 BTUs to heat up your hot water. Because your heat pump can only do one thing, after you heat up the domestic hot water, now your buffer tank for your radiant is depleted, so in addition to heat your house, you need to continue to bring your floors up to temperature, and heat up your depleted buffer tank. So now for a couple hours you need about 37,000 BTUS/H.....It just happens that a 4 ton heat pump is putting out 37,000 BTUs/h. You buffer tank does not store that much heat, just enough to prevent too much short cycling when only 1 or 2 zones are calling. It serves more to separate the flow of water, since your 4 ton heat pump would like 12 gpm, when your radiant system with only 1-2 zones calling for heat might only need 1-2 gpm. Why would I, in this case, put in a 2 ton heat pump with all kinds of backup equipment?

An update on the heatpump install search: We've finally gotten the second bid for our system and have talked with a third contractor we are hoping to hear from soon. Both of these contractors seem to have differing opinions from each other as to the best system, and both are miles away from the first contractor we contacted. It's apparent that there is no settled science to designing a ground source heat pump system - everybody has their own theories and fears. We are still left more than a little confused.

Posted By DickRussell on 18 Nov 2016 08:10 PM


If your house is truly "superinsulated," in that it has insulation levels way above "code," good windows (eg. triple pane), and is very tight (your 0.9 AC50 qualifies), then I have to think that the first contractor's calculation of 40KBTU/hr is way above what your house ought to see, particularly in your location. For reference, our house, built 2010-11, is in climate zone 6 (central NH), is superinsulated, and has two levels on a ground footprint of 2000 sqft. At that time, the regional distributor of CM heatpumps and two of their approved installers all reported heat loads of around 55KBTU/hr and recommended a five-ton heat pump. My own spreadsheet calculation, after the blower door test was first done (0.65 ACH50, final of 0.80), showed 22KBTU/hr. Only one of the installers was willing to provide details of their calcs....

Dick, I have two questions:
1. How much backup heat do you use in a given year - gas or electric - on the coldest days when your 2-ton unit can't keep up with demand?
2. Or, is your SCW basically unlimited in the amount of heat it can provide. The reason I ask, is that your assessment of the contractor's undervaluing of the insulating potential of our house may be spot-on, but we apparently have a different issue in that (according to the second contractor we've contacted) it is our ground loops that are too small. I know I keep repeating myself, but it's still baffling as to why our original contractor actually recommended less pipe length than we installed and a larger, a 4-ton, NSW050 WaterFurnace heat pump, and, now, our second contractor is saying that even a 2-ton unit could very easily freeze the ground enough to damage our foundation. I just keep looking for stories of this happening on the internet, but all we have to go on is the second contractor's anecdotal experience from one job the did a decade ago.

Posted By docjenser on 21 Nov 2016 12:18 AM


You need two tanks, one for the domestic hot water, and one buffer tank for the radiant system to reduce short cycling....
...Why would I, in this case, put in a 2 ton heat pump with all kinds of backup equipment?

Thanks docjenser for an easy to understand description of peak demand. One question for you: Would you still put in the larger unit if you knew that on the coldest nights your loop field was undersized (which we are not sure its is yet)? If I understand part of your recommendation, then, yes, I see your point of installing a heat pump of sufficient size to guarantee a shortened recovery time after a peak demand. But if the loop will be tapped out late in the heating season, as second contractor has said, then will, on balance, it make sense to rely on back up heat for the remainder? Doesn't that defeat the return on investment of an expensive water-to-water heat pump installation?

I keep reading about people in colder climates than ours who have less ground loops lengths than us, who report that their systems work perfectly - and rarely if ever need backup heat. So here is what the second contractor is recommending in his final proposal:
1. The geothermal water to water heat pump quoted is a Bosch TW-035 2 stage compressor with the hot water recovery installed (this feature will provide some domestic hot water heating when the geothermal heat pump is in operation) along with a comfort control module. Included is the pumping center, a storage tank, the pumps and flanges, the piping connections, a low voltage system controller, all necessary components and materials. The hot water recovery feature will require some potable water piping between the preheat tank and the heat pump and can save up to $500.00 a year in operational costs. $12,946.24
2. The connection to the existing radiant floor heat
The connections for the house radiant will tie into the storage tank for the geo system and will include the second stage heat from a tankless to be selected. Because the bulk of the radiant system is in place, the main portion of the install will be to tie in where the existing heater is now. I have priced for 1’’ feeder lines and a pressure and temperature gauge, and the labor to install the materials and components for the geo system.
For this portion- $ 3,951.00.
3. The heat sources
-A Takagi (AO Smith) T-H3-DV N tankless water heater with operating efficiencies up to 94%. The Tagaki can provide both the domestic hot water and the space heating and will be vented using standard 3’’ pvc . The Tagaki has a 15 year warranty on the heat exchanger and 5 years on the rest and is designed to be used in radiant heat applications
Package $3,804.80

The total is $20,701. Even more than the original contractor! And he makes the system sound so elaborate. We had thought that our house would be all electric, especially with our 6kW PV panel arrary. He says that electric will not keep up with peak demand when the ground loop stops giving heat (I assume he means when it freezes), because residential water heaters can only use one heating element at a time, and are thus limited in BTU per hour output - basically he said electric domestic hot water heaters are designed to for occasional load demands for showers, etc. and not for heating your house. That I can understand, but why a tankless gas heater? They are so expensive! My immediate thought after hearing his recommendation is to just install two $500 electric hot water heaters in a row - one would preheat the water for the second and act as a buffer, and that would save us a boatload of upfront money right there.

#2 of his proposal is a little surprising cost-wise. There is clearly something I don't understand here. Our present hydronic distribution system simply has a pump which activates when heating called that circulates water from the hot water tank. Its the simplest part of the system.

So I agree with whomever said it previously in this post, that all the back-up systems of components seem way too elaborate, especially compared to what we envisioned when we first planned the system. We are surprised that with geo-systems costing so much, that anyone can justify the total cost. I am seriously considering just scraping the whole endeavor. My husband is far more trusting than me when it comes to dealing with professionals - he would have just as well gone with the first contractor who wants to charge $19K and be done with it. I'm the skeptic, especially when we get such contradictory assessment of our needs.

On a brighter note, the third contractor we talked with seemed to be the most reasonable in their overall assessment - they basically said that they would provide a buffer tank - when I asked if it could be large, say 80 gallons, he said that would be fine (but he would need to run the numbers to see what our heating and hot water needs would be), and when I asked if we could install a 100+ gallon domestic hot water tank with a heat exchange coil, he also said that would work fine, considering the number of people we often have staying with us at one time. He said it would probably cost under $15k, based on similar systems he'd designed. All sounded good, but, despite his promising to get back to us over a week ago, and me having made several soft follow-up inquiries, we have not heard back from him.

Posted By AlexisB on 09 Dec 2016 01:45 AM

Dick, I have two questions:
1. How much backup heat do you use in a given year - gas or electric - on the coldest days when your 2-ton unit can't keep up with demand?
2. Or, is your SCW basically unlimited in the amount of heat it can provide. The reason I ask, is that your assessment of the contractor's undervaluing of the insulating potential of our house may be spot-on, but we apparently have a different issue in that (according to the second contractor we've contacted) it is our ground loops that are too small. I know I keep repeating myself, but it's still baffling as to why our original contractor actually recommended less pipe length than we installed and a larger, a 4-ton, NSW050 WaterFurnace heat pump, and, now, our second contractor is saying that even a 2-ton unit could very easily freeze the ground enough to damage our foundation. I just keep looking for stories of this happening on the internet, but all we have to go on is the second contractor's anecdotal experience from one job the did a decade ago.

1. As for backup heat, on many evenings during heating season we like to have a fire in the little woodstove on the lower level, to have the warmth down there while watching TV. I leave the thermostat down there at 65. I don't get the stove going until 6pm or so, and the last split goes in well before the 11pm news. Then we let it burn out. Actually, we used that little stove for heating the whole house during the 2010-11 winter, before the heat pump went in. I ran it from mid-afternoon until bedtime, and come morning the interior, up and down, was still mid-50s, having lost a couple of degrees after the fire went out. The work crew didn't want it any warmer. Otherwise, the heat pump itself keeps the house at temperature in just first stage; I've never seen it have to upstage to keep up. We do have two levels of electric strips downstream of the blower, controlled by the zone board. The first level is 1 KW, the idea being it would be used to supplement the heat pump in the event of extremely cold weather, rather than turn on a large strip. The second is the smallest I could get from the mfg, a 5 KW strip. Together, the two strips could heat the whole house in the event of a heat pump failure. In practice, I've never needed either electric backup strip, so the breakers are left off. Last year, it was -14 F one night at 11pm, yet the heat pump kept up in just first stage. The house is never really in steady state on heat loss. It takes hours for the temperature profile across the walls to adjust to changes in outside air temperature, damping the temperature swings considerably.

2. The SCW design needs on the order of 80 ft of water column per ton of heat load. The well will support a three ton heat pump easily, so for a two-ton unit the well is not my limiting factor. You have a different issue, a buried ground loop, and that of course has its own limitations. As the ground around the loops is cooled during heat extraction, conduction from deeper beneath the loops will increase, hopefully to a point of steady state where that rate is adequate for the rate of heat extraction. I will let others comment on loop size required and methods to ensure good contact between loops and the ground for heat transfer.

You loop field is not undersized. Worst case scenario your heat pump will run less efficient. A larger heat pump might put more peak load on the loop, creating a higher delta T between the fluid in the pipe and the ground, thus transferring more heat from the ground to the fluid in the pipe. Overall is does not necessarily takes significantly more heat out of the loop, since due to the higher capacity rest the loop more as well (cycles more). While in general we want to avoid too short of cycling, it is always a compromise between response time, use of supplement heat, and short cycles. I learned to to go higher capacity for water-water systems, the uncharge is minuscule, and the benefit by far outpaces the negatives.

So yes, with your heating load in your climate and the 2400 racetrack loop you describe, I'd still put a 4 or 5 ton (rather a 5 ton) heat pump in. So even if the loop drops down to 25F at the end of the heating season, it is still a much better solution than excessive backup heat.
I just don't see much sense of investing into a geo system, and then put in too expensive hardware for backup heat, which you now much also maintain.

We indeed have less loop in the ground sometimes in Buffalo NY for a 4 or 5 ton system.

To your proposal.
1) I question why you would not make all of your domestic hot water via a water-water heat pump which is designed to make a lot of hot water. Skip the hot water recovery option and invest into an indirect tank (Stiebel Elton SBB400 comes to mind) and a few 3 way valves, and you have a much better solution.
What flow center (pumping center) does the installer propose?

2) Newer piping designs are out there which ties your radiant system not directly into the buffer tank but into the leaving load piping from the heat pump, which saves significant operation costs.
Your installer might not be familiar with it.

3) Again, putting a tankless water heater in is kind of beating the purpose of a geo system, in my humble opinion.

4) Again, there is some silliness. The ground loop will not stop giving heat, dropping in temperature may make the heat pump run less efficient at the end of the heating season, but there is still enough heat there to heat your house. Especially if the heat pump has a larger capacity.....

5) I think I answered the question about an electric hot water tank.

DocJenser, thanks for the reply and we went with the simpler proposal. Water Furnace water heater/buffer tank and Water Frunace heat pump. I realize I'm not quite sure how many tons it is - it's a NSW050 WaterFurnace. Looking at the manual they left, it looks like the "capacity" may be 025. Is that 2.5 tons? Now we have a new surprise - not sure if it really matters, but I can't find any reference to it anywhere online: The contractor has hooked up every other pipe in the same trench to go in the opposite direction. This would be less of a concern if not for three places were the pipes all bunch together - we had quite a number of obstacles to navigate on our small lot. Two of the sections are about four to six feet, and the last one is right before they come into the house, which is maybe 12 to 14 feet of what we thought would be the six pipes return flow direction. I can't say that they are all touching (those pipes are stiff, and without making effort to constrain them, they tend to lay where they want to), but we made no attempt to separate them at those places. We went to see an excavation for loops and laying of pipes in person some 8 or 9 years ago, and those pipes (six straight run pipes, just like our loops) were all joined together with a buried manifold before entering the house. My husband did most of the research on systems, and he does not remember seeing any loops configured the way ours now are. The contractor says running the pipes counter to each other is the most efficient way to extract heat. Seems counter intuitive, but almost right at the same time. He says he is not concerned about the overlap - the total pipe/trench length is 420' (with about 20' not purposely separated), so only a small percentage is laid closely. They have only attached the pipes to their manifolds at this point, but we were not expecting such a crazy mess (see picture). Once again, my husband says to trust the professionals. Anyone know what is the standard configuration for straight run pipes?