I'm in the process of selecting a company to install a geothermal unit,
but we've received contradictory information. I'm hoping this group can
shed some light on the situation.
We've had 2 companies come out and give estimates with 2 more lined up.
Interestingly enough one company based the size of the unit on cooling demands, while the other based the unit on heating demands. If we go with cooling it will be equvilent to 3.5 tons, whereas heating is 5 tons. I"m not sure who to believe. Does anyone have any advice or experience?
Where are you located? Could judge better if had some idea of the climate.
If there's a marked over/under-sizing on either side performance will likely be less than satisfactory. I'd be particularly worried about undersizing heating capacity in a cold climate, however, as if you don't have sufficient capacity there you'll be forced to run on auxiliary ("emergency" in some nomenclature) heat for perhaps extended periods. This will easily negate any hope of ever recovering the initial higher installation cost by lower operational costs.
Had WaterFurnace installation in TN Valley--was very successful at operational cost-effectiveness relative to air/air heat pump conventional A/C unit. That area is, of course reasonably moderate both summer and winter, w/ summer cooling demands normally just a little higher than winter.
I'd get some more input...did the estimators run actual heat load projections or were they simply "back of the envelope" estimations? Authorized WaterFurnace installers have detailed estimating/sizing programs. Other sources of information may be your local power company--many have programs for cost share for energy-efficient alternatives.
I live in Southern Maryland, Waldorf (20601) to be exact. It's about
35 miles south of DC. Both companies are WaterFurnace Installers. THe company that suggested we base the size on cooling load walked through the whole house measuring windows, rooms, doors, and inspected the duct system. He back and said we have 45,000 BTU for cooling and 95,000 BTU for heating. If we put in a cooling load system, the threshold for heating would be 27 degrees. Anything below that we would have to use back up heat.
The second company walked through the house and looked at our current system. He didn't measure anything. He is to call me this week to go over his estimate... but told us we would install based on heat load.
I work for a large HVAC company but they refuse to get into geothermal (I still think they are missing the boat). I know of several companies that do. Could I ask who the two companies are (that did your estimates)?
I'd go with the first guy who sizes on cooling load, especially if you have high summer humidity levels. Normally the backup heat will be auxiliary heat. It will run IN ADDITION to the Water Furnace, NOT instead of it. The operational cost of some strip heat usage should not hurt too bad. With geothermal, the heating capacity won't degrade with the weather. The first guy did the survey properly, I think you will be happier with him AND his installation.
If it's set up that way...the fella' that did the installation of ours put an external thermocouple in addition to prevent them from cutting on before about 25F...but even then, I don't think we ever had them come on for any extensive period except once when it got to -20F (in Knoxville, TN area, no less!). But it was sized for heat load, essentially. It actually was a little large for the cooling load, but not so excessive to be a real problem.
I recommend the WaterFurnace highly, btw, as long as the installer is really experienced...cut operating cost to nearly a third of what the air-to-air heat pump had been--of course, it was an old, cheap unit.
We're in southernish Ontario (Ottawa). The one Geothermal dealer we spoke to (there may only be one in our area ;-( sizes for heating load.
[Roughly 1 ton/800 sf, one hole per ton.]
What you should do is ask the guy doing "cooling load" estimate how much backup electricity you'll use.
There's another factor to consider - the geothermal will shut down even if it's above the threshold if it figures the ground loop has made itself too low. So an undersized unit may "freeze out" it's heat exchange branches during sustained low temperatures, and effectively not work at all.
And with many properly installed / sized geo units operating with a COP of 4 or better these days, then if / when the system defaults fully to the backup heat strips then it's well to remember its gonna cost you 4 times as much to run at capacity.
If that happened at all frequently, that would indicate the loop is either too small or not deep enough. In Canada, of course, the ground cooling is much more significant than it was in TN where I was or in MD where OP of the thread is. Being "that type of guy" :), and one of the first non-lake-loop installations the local fellow did, we put thermocouples on the loop piping at the intermediate- and bottom-of-trench levels at the inlet and the outlet ends and monitored them for a couple of years. IIRC, the bottom of the trench was ~6 ft and didn't change but about 7F from mean during the year. The mid-level was more like 12-15F. These are a long time ago, but I think that was pretty close...
If it's at all capable of doing so. We had a geothermal company out, and they were spec'ing it with a mere 5Kw of backup heat. Which if the geo primary goes out, you're going to freeze.
[We could only get away with that because we have _baseboard_ heat, and we weren't planning on tearing it out.]
Ottawa will be slightly worse than MD, but probably not by that much.
As a FYI: I don't think they do horizontal loops here. For each ton of heating, they drill a 100' deep 3" diameter vertical hole. IIRC, they were 10' apart minimum. As it was explained, at peak loading, you might "lose" a small amount of available operating time due to freezing the ground.
I gather that it's not too hard to dig there...in TN that would be bedrock and pretty expensive drilling...but I'd agree the deeper the better...as noted, at the time I put in the system in TN, the only local installer was almsot exclusively working in a development on Tellico Lake and using the "loop in lake" ploy...
It'd be bedrock here too. We're on the Canadian Shield ... Granite, quartzite, with relatively shallow sedimentary overburden in places. Probably very similar to TN - old hard rocks.
That's not geothermal. That's a water-source heat pump. There's also ground source heat pump that operates by circulating an anti-freeze or alcohol solution through pipes buried in the ground - either in trenches, or in deep holes. Or, ones that pump water out of the ground (and either back into the ground, or simply dumping it on the ground) for their heat source.
Geothermal is slightly different. Geothermal is where you put the exchange coils of the compressor _itself_ underground. Rather like unravelling the plumbing on the back of your fridge and burying it. These things use "real refrigerant" (often a freon of some sort) in their buried loops. Not a heat exchange liquid.
These are more efficient than water-source heat pumps, because there's only one loop rather than two. One heat exchange interface, not two.
Exact same technology, only different hear sink...all I did was mention the system we did was this particular installer's ground instead of water loop....
There's many different kinds of freon, some of them are bad for the atmosphere, some of them aren't. The treaties are on _specific_ freon compounds - R12 is one of the baddies.
PremierE WaterFurnace uses R410-A for example.
Here's a link - it shows the more traditional heat pumps as well as the full geothermal types.
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Some other closed systems use ethanol or methanol. (They've decided to not permit methanol in Ontario).
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