OT - Geothermal Heat issue...?

Page 1 of 5  
Howdy,
This is way OT...(again), but:
We heat and cool our home geothermally (water to air system.)
We would, of course, like to decrease our costs further if we can, and so have explored the benefits of setting our thermostat lower at those times when the house (or parts of it) are not occupied.
The folks who designed the heating system say that with these systems, it is best to leave the set temp unchanged.
Of course, I have asked "why", but when I do, it seems that smoke starts to come out of the phone. In essence, they say that it is "best" but seem unable to say why.
Might any of you know what would be best in this regard , and particularly whether the issue of thermostat setback is actually any different for geothermal systems?
Sincere thanks,
--
Kenneth

If you email... Please remove the "SPAMLESS."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Cycling a building in and out of extremes will bring into play the building's phase. The lower extremes may force the auxiliary heating to start up (maybe electric?). It might be cheaper to keep things at a low wick rather than replacing lost heat with expensive heat.
Just a hunch.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Robatoy wrote:

The need for the aux heat should be minimal at most for an adequately-sized geothermal system. Some t-stats may demand it if the temperature differential from setpoint gets too large, though, so it should be ensured the rampup doesn't force that.
In general, the same rules apply -- a setback at night, for example, will result in a lower average temperature so the effect is still there.
As a side note, had a ground-loop geothermal system in TN and liked it a bunch. Am considering it for a replacement here...
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Hello again,
Your reasoning is similar to mine...
We do not have any auxiliary source of heat: Our (9 ton rated) heat pumps are more than sufficient to do the deed even at 20 below.
For the life of me, I can't understand why the folks who design the system say it is best (that is, less costly) to keep the temp constant.
One possibility that I have thought of:
The cooler the water in the well, the lower the efficiency of (and thus, the higher the costs of running) the system.
Suppose that each night, we allow the temp of the house to drop, say, 10 degrees F.
Then, in the morning, lots of energy would have to be extracted from the well in order to rapidly bring the house up those ten degrees.
That would (obviously) cool the well, thus decreasing the efficiency of the system, until the house warmed up. As a result, the costs per BTU would go up during that period of (relatively rapidly) re-heating the house.
Assuming that reasoning to be correct, the issue boils down to whether the cost of that loss of efficiency is greater or less than the savings to be had with the lower overnight temperatures.
Thanks for any further thoughts,
--
Kenneth

If you email... Please remove the "SPAMLESS."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Kenneth wrote:

All depends on the capacity of the well and how the loop is configured. Unless the well is stagnant and of marginal size and the exchanger is closed loop, I would expect that to be a minimal problem. If the well weren't a well but a closed tank, maybe, but that's unlikely to be a realistic model. Would have to know more to do a real calculation/estimate, but I think it's not likely such a big issue.
I have been told by one installer here that owing to our very dry climate there's an issue w/ ground loops and heat transfer. I've not yet delved into it in sufficient detail to decide whether I think that's hokum or not -- this guy hasn't yet actually installed a system, he's just going on what somebody else has told him.
Would be interested in the capacity of the well, amount of exchange tubing, etc., to support the system you have as a comparison. They wanted to punch two or three holes here for deep ground loop, but at $1500/ea, that gets terribly pricy quickly. Would have to have a second well to go that route, but I'd think it could be only one although it would not suit me to have it be a once-through in an arid area.
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Hi again,
Trusting my memory here...
Our well was designed for the 9 ton capacity. It is 460' deep, and is 8" in diameter. It has a sleeve for just under 400'.
All the best,
--
Kenneth

If you email... Please remove the "SPAMLESS."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 26 Nov 2007 15:55:03 -0800 (PST), Robatoy

Howdy,
There is no auxiliary heat...
So, whatever heat energy lost by the house is replaced by the heat energy extracted (at some cost of electricity) from the well water.
My reasoning was that keeping the house warm when empty would have greater cost than keeping it cool when empty (that part seems obvious) and heating it up to comfort would take less energy than that which would be lost were it kept warm continuously.
What am I missing?
--
Kenneth

If you email... Please remove the "SPAMLESS."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You might want to verify that...
Our WaterFurnace heat pump maintains temperature very well when it drops to below zero here in central Ohio. But if you raise the thermostat by more than two degrees at a time, the auxiliary heat coils in the "furnace" do kick on, and the electric meter spins like crazy until the house temp is back within two degrees of the set temp. In our case, the "auxiliary" heat is for quick temperature changes.
This is different than our old house with an air-to-air heat pump, where the auxiliary heat came into play whenever the outside air was too cold for the pump to generate sufficient heat. Fairly often, in other words, since air-to-air pumps lose efficiency as the temp drops.
To use a setback thermostat, we would need one that raised the temperature only two degrees at a time and/or would need to disconnect the internal resistance coils. We are satisfied with a fixed temperature of 69, and heating bills that are a third the size of friends who have gas heat and homes that a half the size of ours.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 27 Nov 2007 01:36:07 GMT, Larry Kraus

Hello again,
Other than repeating it, and assuring you that I know what I am talking about in this regard, there is little more I can do.
When we installed the system, we discussed this issue at length with our contractor, the designer is the system, and the system's installation folks.
Based upon their input, we opted for a design with capacity sufficient to eliminate the necessity for any auxiliary system. In fact, there is a box in the air handler that would allow for the installation of such a resistance heat supply, but it is empty.
All the best,
--
Kenneth

If you email... Please remove the "SPAMLESS."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Larry Kraus wrote:

The thing to do is to add an exterior thermocouple to the aux heat control so the aux heat doesn't come on unless exterior temperature is at some preset temp. This can eliminate the mostly gratuitous usage.
What we did for the Water Furnace unit we had. (Unfortunately, I had completely forgotten doing so and when we had moved and the new buyer's inspection showed up the elements didn't work, I was gone and we ended up w/ a service call to re-enable them to close the sale. :( ).
Anyway, there was also a setting on the thermostat that overrode the "high" heat setting that could be used as well. Seems like that thermostat was an option over the base one that came w/ the unit, however. It had a setback option built in this worked with iirc, whereas the other was a simple setpoint t-stat. This is quite a while back now, memory's getting dim on precise detail.
I agree the units are well worth the initial extra installation cost, particularly if don't have relatively cheap gas available...
--

--

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Hi,
As I described just above your comment, we do not have auxiliary heat at all.
All the best,
--
Kenneth

If you email... Please remove the "SPAMLESS."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Kenneth wrote:

I was responding to the guy who does, not you...
-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It keeps coming back to the building's phase. It doesn't cycle at the same speed your internal temperature does. As you turn down the thermostat, the building's stored heat is given up, some to the interior, but some to the exterior (loss). To reheat the building's interior, the heat is not only heating the interior, but also the building's mass. So, when you turn down the thermostat, you need to later replace the heat you lose. Once the building is up to temperature, you just overcome the building's heat loss...like Lew's Ball.
I was going to try to equate this with the reason why when you increase the waterflow through your car's radiator by taking out the thermostat, your engine will overheat. The water HAS to spend time in the rad to be able to give up its heat. So the thermostat slows down the waterflow. Conventional thinking would suggest that by increasing the waterflow, it should cool better. (There are a few caveats in there too, so everybody keep their shirts on.)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Robatoy wrote:

...
No, you don't need to "replace" the heat you lost for the period the setpoint was lower -- that's the gain.
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Only if you decide to keep the building's mass at that temperature. If you want to restore the temperature of the model, you also have to re-heat the container.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Robatoy wrote:

But the time at lower setpoint more than compensates for the differential loss. It's well-established in general that a setback lowers overall heating costs in general. It would take unusual circumstances for that to not be so.
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Hi again, OP here...
That is just what I am trying to sort out:
For reasons that I have not been able to understand, the Geothermal folks say that for their systems, it does not work that way (and they seem to be consistent on this.)
All the best,
--
Kenneth

If you email... Please remove the "SPAMLESS."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
dpb wrote:

It's not something one should just assume. Especially with alternative energy.
--
--
--John
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 27 Nov 2007 11:31:32 -0500, "J. Clarke"

Hi John,
Might you know of some reasons that the general principle of savings through setbacks would not apply to my geothermal source...?
As I have said before here, I certainly do not (know enough to) disagree, but I have no understanding of why that should be true.
Sincere thanks,
--
Kenneth

If you email... Please remove the "SPAMLESS."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Kenneth wrote:

I don't think it is, in general, any different unless one of the conditions outlined previously were to be true for a given installation.
I've not looked recently, but when we were looking into it initially, Oklahoma State was the leading research university on geothermal. I'm sure there are many others with useful information that a google would uncover as well. The other place that had a wealth of geothermal information online back then was also TVA (tva.gov). I would also expect the EIA and DOE energy conservation web sites to be potentially useful as well. You might try Water Furnace directly rather than the local distributor/installer to see what they say -- I found them to be quite knowledgeable with their evaluation/sizing software packages. It wouldn't surprise me at all but what they could actually make that a part of their analysis for your particular system -- of course, being as it is already installed, they might not want to run another gratis...
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.