Climatouch offers a tstat that will do this for you.

I was unsure if it I should raise these questions in this or a new thread, but listed it here.

I'm trying to understand this better and need some help (I was going to say I need professional help, but that doesn't sound very good!)  This is a heating question, but I am also wondering if the reverse is true for cooling:

1) Will it take longer for a system to increase the house temperature by a given number of degrees the colder it is outside (compared to when it is warmer outside)?  For example, it may take the system 8 minutes for a 3 degree increase when it is 55 degrees outside, but it will it take longer if the outdoor temperature is 20 degrees?  Why?

2) At a given outdoor temperature, will it will take longer for a system to increase the house temperature by a given number of degrees the higher the indoor temperature is?  For example, it may take the system 8 minutes for a 3 degree increase from 66 to 69 degrees, but will it take longer for the system to increase the temperature from 71 to 74 degrees?  Why?

Thanks!

I'm no pro but I'm a homebrewer so I heat enough liquid to know this one:
1) It will take longer to heat the home with just the geothermal unit the colder it is outside because the ground temperature will be colder in general due to the air temperature. This may be nominal. But, also, the ground will be colder because your unit is running more and dumping more cold into the ground. Those here who monitor their systems report that ground temperature does fluctuate even on a well designed system. 18 degrees F up or down from surrounding ground temperature is reasonable from what others have posted. That takes your efficiency down on the geothermal. As far as the electric units, they will always perform at the same efficiency, 100 percent.

2) It will take longer the more your house is from the outdoor temperature. It takes less energy to take a unit 10 degrees from air temperature than it does to take it from 10 degrees to 20 and so on. Watching water boil, you'll notice it gets hot in no time but take a long time to actually boil. This is also why setting your hot water heater to 120 F instead of 130 F saves you quite a bit of money. The higher you go the more energy it takes to continue.

In sum the greater the load (heating or cooling)- the longer it takes to satisfy it. Also as pointed out the smaller the disparity between ground and outside air temperature, the longer the unit has to work.
Multi stage units are designed tight so in extreme weather heat pump may operate most of the time in first stage, often in second and if heating dominated more than a little in third (aux).
joe

Thanks, Joe! I've heard that before from somewhere, but I was never sure...it's good to hear it confirmed. In my last house, I had an air/air heat pump which I'm sure was oversized. It warmed the house up fast and cooled it quickly, but so fast that it would turn on for just a little while, then shut off.

I'd heard that heat pumps need a little time to reach maximum operating efficiency, something like at least 20-30 minutes. It's actually more efficient (if I read that correctly) for stage 1 to be running much of the time, rather than a constant on and off.

I think my next steps are to get an outdoor sensor (about $20) and wire it up to the thermostat, then set the aux cut out as low as possible (40 degrees) and put the aux breakers back on. I'll carefully monitor the system for aux heat use.

I also just contacted my elec company (Excelon/PECO) as they give a reduced winter heating rate for heat pumps.

Another thought...
Wouldn't it be better to hook up a temperature sensor for the ground/ground loop to the "outdoor sensor" of the thermostat for the purposes of aux cut out? I mean, if it's a true outdoor temp and the air is 32 F, but the aux cutout is set for 40, even if the ground loop is 50, the aux heat would come on. I think it would better to measure the ground temp, preferably NOT the coolant in the pipes from the ground since when the system calls for heat, the pumps might not be circulating at that moment and the reading would be false. I should have buried a sensor in the ground, 100 feet down or something, hooked that to the thermostat, called it the "outdoor sensor", reactivated the circuit breakers for aux heat (in case the GSHP has a fault and requires aux heat), and used the ground temp as the cutout temp for aux. Darn it. How can I bury the temperature sensor now??

In my opinion, the problem isn't the outdoor sensor. The problem is that your thermostat won't enable the aux lockout to be set lower than 40 degrees. Our lockout will go as low as 5 degrees F. At some point, the outdoor temperature will drop low enough so that your geothermal system won't be able to keep up, unless it was designed to provide 100% of your heating needs. Your installer can tell you the (estimated) balance point that your system was designed for. This will give you an idea of what the "real" outdoor temperature may be when your system will run 24 hours a day and simply cannot contribute any more toward heating your house if the outdoor temperature falls further. At this point, you have a choice of letting your set point drop, or using some kind of aux heat to supplement the geothermal system.

I looked at the Climatouch manual (good find Dewayne). Personally, I like some of the features on the Climatouch, but I prefer a thermostat with an aux lockout better.  It doesn't appear to me that the Climatouch has an aux lockout feature based on outdoor temperature.  I know my aux won't go on unless the outdoor temp is below the lockout temperature regardless of my nighttime setback. With the Climatouch the outdoor temperature doesn't directly impact the aux heat. Rather, the aux heat goes on when the thermostat can't keep up by the specified number of degrees you set in the advanced settings. As far as I can tell, aux heat can still go on if you set back the thermostat more than the amount of degrees you specify for the aux heat.  The Climatouch manual I looked at was for model CT0-7TC-32H.

My non-professional advise is to either:

a) if you can afford a new thermostat, get one with an aux lockout setting that can be set at least as low (or significantly lower than 40 degrees) as your system was designed for (without aux heat) and get a compatible outdoor sensor (wired or wireless). You can justify the price (we did) with the savings that you will receive from not having the aux heat unnecessarily go on year after year.

OR

b) if you can't swing a new thermostat right now, turn off the aux breakers but REMEMBER TO TURN THEM BACK ON if you go away for any reason for more than 24 hours. If you have to leave in a hurry for an emergency, remembering can be a problem. Might want to mention it to a relative or neighbor that has access to your house so they can help you remember and turn the breakers back on if necessary. Clearly label the aux breakers in the breaker panel.

If your system is very new, see if your installer can credit you something toward a different thermostat since the current one may not suit your needs as well as a different one.  If they can't help you, professional thermostats can be found on the web for a discount.  Make sure the new one has the aux lockout range you need (by checking the online manual) before you buy it.

Lest we forget, discuss this with the installing contractor. If system fails to perform in February, that's a bad time to learn that disabling the aux. took heat from the ground more quickly than it can be replaced.
J

Wow, how are you getting 105 degree vent air? That is a 40+ degree temp rise and way above the specs which max at 30 degrees best case with 50 degree entering water.  

All I know is that the HVAC guy has a sensor installed right at the top of the unit (just above the aux coils, which are turned off at the breaker) wired to the zoning control....I guess maybe it's used to help tell the unit if it needs stage 1/2/3 heat, and it's reading 105. He also showed me on a handheld sensor that he poked into the main supply trunk about 10 feet down the line, and it, too, was reading 105. The air coming out is VERY warm to the touch, and I swear that Aux heat is not even possibly on. I guess I could stick a thermometer into a register and triple-check that. I'll report back. Loop temps today were 47 degrees. That seems cool.

One simple and inexpensive way to prevent premature operation of aux heat is to introduce a time delay on the call for aux heat. Adjustable timed delay on make relays are available. Adjusted to the delay of your choice (based on a balance of your comfort and  desired efficiency) the heat pump has more time to catch up when you bump the tstat.

The biggest advantage to this strategy is that aux is "locked out" only for a reasonable period of time but not long enough to freeze up the house.

Some thermostats can do this and Energy Star is working on a new specification that requires some control over this situation. However I would not buy a tstat based on this feature alone when I can use the tstat I have and do the same thing with a $20 relay.

As always one should contact their installer before interfering with aux. heat. As noted systems are tightly designed and tight loop fields may make you wish in January you hadn't disabled aux heat in December.
You also want to avoid "fools gold" of avoiding auxilliary now and reducing average COP throughout winter (by accelerating ground temperature drop). Maybe set it and forget it can be the least expensive operation policy (in heating dominated climates with closed loop systems and auxilliary designed in ....results vary....consult a physician before use).
Joe

That's a pretty cool idea, and fairly simple....I guess I would somehow "tap" the wire from the zoning/termostat panel (where both thermostats connect) that sends the call for aux heat, and that would trigger some sort of timer that would then energize a relay, completing the original aux heat call. Is there a chip/circuit that you could recommend? A couple of NPNs and a large cap? I could probably build it myself, even if it was just a 5-10 minute delay. I like the relay idea, too, because I could use a DPDT and wire some sort of "alert" to the other pole to more easily see when Aux Heat is coming on. That siren I mentioned in an earlier post, for example. :-)

I don't know about the other guys, but time delay relays have caused me more trouble than almost anything else....
j

This is the first time I've heard of needing to worry about accelerating ground temperature drop. I mean, the whole "sell" of geothermal is that the ground is "a constant temperature once you get more than 10 feet down". Here, I have 2 300 foot wells, but I still need to worry about not getting enough heat?? I'm not sorry that I got the system, I mean, even if ground went down to 40 F, it's still better than the air at 30 or lower, but my HVAC guy never even mentioned about ground temp drop. I still think my next best step at this point is to buy an outdoor sensor, wire it to the termostat, activate the aux lockout as low as possible (40 F) and leave the aux heat on and available. At least for much of the fall and early spring, the aux won't activate unless it's really cold outside. I'll be curious to see what the bills are for the winter...as long as I get less than $300/mo, I'm making my money back.

On another topic, anyone explored some sort of system to bring outside air in on spring/fall days for cooling? Something like a zoned control but the zone opens a vent to the outdoors and sucks air into the central return, assuming it's dry, non-humid air?

J

LOL, you mean I have to MANUALLY open the windows??? Can I get electrical window actuators (openers) so that they slide up and down automatically? Seriously, I guess I was thinking at nights or when we aren't home, that the system would "know" and use outside air if/when appropriate. The downside is, of course, the cost vs. the payback for such an "economy" mode for cooling.

It makes sense about the heat replacement in the ground...I'm seriously learning so much about ground loops that I ever thought. What I'm finding with any system is that most HVAC guys know how to install a system, but don't always know how to fully tweak the system for absolute maximum performance. I mean, all my ducts have in-line dampers, but when I asked the guy whether they need adjusting/balancing with the new system, he said, "You can adjust them if you want". I always thought that the HVAC company should know/do that sort of thing to balance the air flow. I did open them fully and am VERY happy so far with the performance of the system. I guess I'm just a geek who's trying to turn an A+ system into an A++ system. I will ask him about the outdoor sensor, just to get his thoughts before I order one.

Contractor installers do not maximize your features as value added is lost on most and opportunity for call back is greatly increased due to accessory breakdown or user confusion. If you want to maximize your system get a monitor such as wel server or at least monitor ewts and you will be able to glean if your loops will keep up with aux. off. Just remember lengthy compressor cycles can cost more than short aux cycles. We've been asked before if 1st stage is so efficient why not oversize equipment so that 2nd stage isn't necessary to which I respond they have heat pumps like that they're called 1 stage. If you look at aux. as 3rd stage and not the enemy you might find that it can add to efficiency by letting you run a smaller compressor all the time. J

Ok, temperature update. Just now, the indoor temp is set to 69F. Outdoor temp is 57F. Loop temp is 49 F, air at register: read using a digital oral thermometer is 92.7 F.
Thermostat is VisionPro 8000.