Heat Pumps for Hydronics

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Heat Pumps for Hydronics

Ground source heat pumps are the coming thing for energy efficiency. And they are a natural step for expanding the hydronics industry.

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cherylm

Is there a heat pump/exchange system for hydronic baseboard systems? If so, where can I find out more about it. I am in Nova Scotia. And how cost prohibitive is it, I am on a fixed income.

Jamie Hall

The best comment — not really an answer, sorry! — I can give you, @cherylm , is… yes, sort of. Search for information on air to water heat pumps or ground source to water heat pumps. The reason I say "sort of" is really two fold: first, the available hardware is changing and developing very rapidly, and applications which were out of the question even a few years ago are now at least feasible, if not entirely practical. The other is that the applications themselves are widely variable. Consider only what might be your own situation to see what the variables might be! I don't know where in Nova Scotia you are or what your house is like, but let's take two examples which are more or less extreme: you might have, let's say a modern construction, well insulated, tight house in a protected, sunny location near Digby, with quite a bit of baseboard. Or you might have an older house exposed to the wind on the coast near Cheticamp with minimal baseboard. The two factors involved are first, the difference between outside conditions, which affect how much heat you need and, for heat pumps, how well they can heat at all, and the temperature of the water in the heating system needed to get that heat to you. In the first instance, the outside temperature may never get much below -10 Celsius, so a heat pump will still work well, and there is enough baseboard so that the hot water needed to heat the space need not be much above 50 Celsius. A modern air to water heat pump can do that quite reasonably. In the second case, the outside air temperature might be -20 C, and due to the relative lack of baseboard you might need the circulating water to be even as hot as 90 C. Which even the best modern heat pumps can't hope to do.

Then there is the question of cost. A heat pump will be more expensive to purchase, install, and maintain than a fuel fired boiler powering the same system. However, it may be less expensive to run. This latter factor is, again, widely varying depending very much on the relative cost of electricity vs. available fuels. In my own specific location (northwestern Connecticut), the relative cost to run at various temperatures is such that oil fired steam heat is less expensive at any outside temperature less than about -2 Celsius — because electricity rates are very high, and oil is still quite reasonable. As they say — your mileage may vary! What makes the calculation a little difficult is that the amount of heat a heat pump can produce per kilowatt consumed varies with outside temperature over a fairly wide range, while the heat output from a gallon or cubic foot of fuel doesn't vary at all.

To finish on a practical note: unless you have a tight house in a relatively sheltered location, reasonably priced electricity, and your existing system is running well, keep the existing system. Apologies for being long winded!

DCContrarian

There are two issues working to prevent the adoption of earth-source heat pumps.

The first is a short-term issue. Earth-source is a niche market, there are fewer product offerings and new products come out slowly. The entire heat pump industry is undergoing rapid change and technological innovation, and those innovations are slower to reach the relative backwater of the earth-source heat pump business. So things like variable-speed compressors have been commonplace with air-source heat pumps for over a decade still haven't made their way to the ground-source world. Variable-speed circulators are basically standard with air-to-water heat pumps but aren't yet offered with water-to-water models. So while earth-source has a theoretical advantage in efficiency, the reality is that the actual products being offered today are close to on-par with what air-source has to offer. Given the cost difference it's hard to justify ground source. Now, this is a short-term issue, presumably in time these new technologies will be taken up by earth-source manufacturers.

The long-term issue is that for ground-source you need a hole in the ground, and anyone who's ever dug a hole knows you never know what you'll hit. I saw a study recently that a significant portion of earth-source wells are undersized for the houses they serve. Not because they weren't properly engineered, but because the engineering mis-estimated the thermal properties of the underlying soil. The study defined a well as being undersized if in the heating season the ground around the well would freeze. Ice is a much better insulator than liquid water and frozen ground is a better insulator than unfrozen ground. So if a well starts to freeze because more heat is being taken out of it that it can supply, a chain reaction begins. The freezing reduces the capacity of the well further, which accelerates the freezing, until the whole well is frozen up. Once that happens it's easy to get into a circumstance where the well is colder than the above-ground air, which completely eliminates the appeal of the ground-source system.

Jamie Hall

Excellent comment on ground source heat pumps and their problems, there, @DCContrarian , though I would be inclined to say that if the well freezes — or even comes close — saying that the system was "properly engineered" just isn't correct.

To which I would add: determining the available heat from a well is a job for a hydrogeologist, not an engineer, however well meaning the engineer may be. Further, it depends on the type of heat exchange envisioned. The testing and analysis required for a pump and dump scheme is very different than what is required for a closed circulation well, and the latter is much less well understood at this time. Engineering a buried grid closed system is actually a good deal easier; unfortunately they take a lot of pipe and a lot of area — never mind enough depth of cover over sundries like bedrock…

leonz

All it takes is one pin hole leak in a chain of shallow grouted wells like the ones drilled for the City of Auburn, New York. Thermally enhanced grout has clay in it which is a net insulator to begin with.