I have a Climatemaster geothermal system with 2 heat, 2 cool and resistive heat which is just a 3rd heat.

What I need is a 24 volt signal to operate a small relay when the GTHP is in any heat mode.

I am running solar glycol through a heat exchanger which is installed in the GTHP ground loop but I only want the heat exchanger working when the GTHP is using heat and the loop pumps are on.

I will use two relays in series with the one receiving the signal that the GTHP is in heat mode and the second 240 volt relay will be connected to the ground loop pumps. This will provide a signal to the solar system when the GTHP is in heat mode and the ground loop pumps are on.

Thanks,

John

I think I figured it out. Not sure if I need two relays for Y1 and Y2 but my guess is that I do.

Y1 and Y2 are compressor stages. They'll be energized in either heating or cooling mode.

The compressor doesn't reverse upon mode change, rather a special valve redirects both sides of the refrigerant flow.

That's the signal you may be interested in to differentiate between heating and cooling.

It is typically "O" for Orange as you have noted. Many but not all systems energize "O" for cooling, if memory serves.

A thermostat will leave the Y1 call in when Y2 is called for so you will not need a Y2 relay. Other than that it looks good to me.

BTW that's an interesting concept. Just how did you connect that heat exchanger and where? Do you plan on collecting data? Let us know how it works.

I used the manual to come up with the wiring schematic. Orange is the reversing valve.

thanks.

I will collect data using hobo data loggers, I already use them for the outside air temp and for the geothermal system measuring the loop temp in/out.  I also have kWh meters that report to a spreadsheet for the GTHP and seperately for the water heater.

I will take a picture of the heat exchanger but it's a SS shell & tube design but a bit different. It has a shell with 1.5 inch connections on either long side but on the inside is not the normal fill of tubes but rather one simple swirl of ss pipe which is the solar glycol loop. Reason for using this type of exchanger was to maintain the flow rate in the ground loop which is pretty high at over 12GPM.

The exchanger is in the return to ground loop line. With the flow rates so high even with the three panels getting a lot of sun it still will only move the water temp in the return line by 3-6 degrees which will help maintain a warmer EWT and increase the efficiency of the GTHP.

 

I will prove my theory as this being a good idea or I will let the solar hot water heat the DHW and the heat dump which is a air/water exchanger plumbed in the HVAC basement zone. I will use kWH along with heating Degree days and the data from the data loggers.

 

It seems to me that the worst month for the geothermal is February and because that’s when the EWT bottoms out. The solar might be able to counteract that since we get a lot of solar energy starting in February.

 

I may use more control by not allowing the solar to go into the ground loop when the ground loop is above a certain point maybe 40 f. Reason is that if the EWT is 40 or 45 the amount of heat is about the same from the GTHP. It’s a work in progress and will take lots of experimenting.

John

New diagram.

Looking at this closer I think the Y1 relay could be eliminated too and just use the pump relay since it  should only come on with the compressor.

The exchanger is in the return to ground loop line. With the flow rates so high even with the three panels getting a lot of sun it still will only move the water temp in the return line by 3-6 degrees which will help maintain a warmer EWT and increase the efficiency of the GTHP.

I wonder if it would do better if it were in the supply to the unit?

 

No. It's more efficient at the return side because the temperature is at it's lowest point which increases the delta-t of the solar glycol. The ground loop in/out of the GTHP delta-t is 4.5 degrees on average when the temperature of the EWT is 40 f. In the end the design is to add heat to the ground loop which will give the ground loop a break, if you will. It will allow the temperature of the ground loop to increase and that's very good for geothermal especially in February. I had originally designed a system that would have more controls and would actually take control of the ground loop and heat it even when the GTHP was off. In the end what I did seems easier/simpler and has little bearing on the GTHP. It is a great system because even today while the sun was in the clouds I still get 110 degree water off the roof panels and it heats the water in the DHW to about 103 f and then the water flows through the heat dump. The heat dump is in the HVAC basement zone and since the fan runs all the time the system is heating the 2,400 SQ-ft basemnet. The heat dump also has it's own fan and aquastat so if the water gets too hot it will blow 700CFM accross the coil. Attached is the design. I have left out the safety controls and such but they are there. John

Kudos to you for that. I love simpler and you did it. You just saved me 10 bucks because I didn't see that. I still didn't get around to doing this and thought I'd do it tomorrow. Thanks for thinking... John

New Diagram.

Nice set up John

I worked with an engineer (no offense to anyone) who said that would not work because the ground would just absorb all the heat. I sorta thought that was the idea behind it. I noted that you have vertical loops. I wonder if horizontal would be any different?

I would love to see how this works out as you progress.

Keep us posted.

I've been wondering the same thing...

I've been told more than once that it won't work but we'll see. You just have to remember that the water in the ground loop leaving the solar GTHP heat exchanger will still be lower than the ground temperature. It will take the stress off the ground and thereby let the ground recharge but it will not be warming the ground.

John

This system is a good idea but it will depend on how low your EWT goes in the last part of winter, February. If you have a loop that is in water
or is an open loop this won't work well. If your EWT does not go lower than 10 degrees from static don't bother, use the solar to shut the
GTHP off instead. I will see my EWT go down below 35 degrees from a static of 48. If you have charts for your GTHP you can see the effect
of lower EWT and you can see what I call the GTHP snow-ball effect. You need 30K BTUs and at 40 f EWT you got it and the unit cycles. You
now need 32K BTUs and the unit cycles less and the EWT falls 2 degrees and now you only get 30K BTUs and you really need 32K BTUs. As your
EWT falls your delta-t from the loop goes down and this means less heat.

If this works it would work for all those people that have resistance heat going on in February and it will help keep the ground loop healthy.

It has been written that the ground loop should not go lower than 18 degrees of static or you will loose more each year.

It's all interesting.

John

Jongig (John) - Please don't get me wrong, I very much like your idea and am impressed with how inventive it is. OK now don't shoot me. Suggestion/Question: Would efficiency increase if you stored the solar BTU's in a mass storage tank? And run the entering side of the Geo loop through a heat exchanger in that tank? For the cost (and space) of a large insulated storage tank, the solar BTU's would be spread around the clock and any loss occurring in the earth loop would be eliminated. Does this make sense or is it too simplistic to work?

An addition to your system which modifies loop EWT according to the changing environment, can you make a system on the air side that changes zone priorities and capacities depending on heating or cooling modes? This would be useful in homes with two stories. More heat needed downstairs and more cooling needed upstairs etc. My house is a good example because of the huge vaulted living room.

Thanks,
John

John S

I agree with the idea in paragraph 1 - heat gathered from solar is likely to be of higher 'quality' (temperature) than heat from the ground, so ideally it is retained and used as directly as possible in the home, not dissipated into the ground. I also wonder if the capital costs and additional running costs of the solar assist would ever pay off in increased efficiency / reduced operating costs.

Conventional zoning should accommodate variable loads summer and winter, upstairs and down, as long as it is properly designed (that is, ductwork for each zone sized for that zones highest CFM requirement) That is the central purpose of zoning. By recognizing the diversity of the load, i.e. peaks occurring at different times of day, zoning sometimes allows a slightly smaller total system capacity, which in turn helps the zoned system cope with part loads. Zoning must additionally be designed to accommodate minimum airflow needed by the system in low stage.

No shooting here, I'm a nice guy. I think the system you describe is a good possibility and I sure like the idea of starage. It will take me at least a year to decide if routing energy into the GTHP loop is a good idea. From what I see so far in the early stages I've notice some good and some bad. Zoning is rather easy and if you wanted to direct heat to different areas using a HVAC air system it would not be very hard. I have 4 branches from the main plennum and I took the one which is in the basement and placed a air/water exchanger into it. I could place them into other branches and zone control each branch. I've noticed that homes with vaulted ceilings usually don't have a return at the top and they should, IMHO.

The good: At the early part and late part of a sunny day the temperature off the roof is only 80 f and the delta t of the heat dump is about 5 f and the flow is 2GPM. After calculating you get about 5,000BTU/h. If the GTHP turns on the Delta T of the solar glycol increases to 15 f and now we're at 15,000BTU/h from the solar system. The GTHP is producing about 30,000BTU/h and so is getting about half from the solar system.

This shows more production in BTU/h in my system by a lot.

The bad: The solar glycol was up to 130 f today and while the GTHP was on the Delta t went up to 20. When the GTHP turned off the solar water heated up the 50 gallon storage tank from 101 to 119. Then the differential control directed the water to the heat dump. The delta t accross the heat dump was over 15 degrees f. The heat dump is in the HVAC system and the HVAC always has at least 700 CFM from the fan being on.

This gives me the idea that at higher solar temperatures I might be better off not letting the GTHP have the solar heat. With heat in the HVAC system I'm using less electricity and maybe keeping the GTHP from turing on at all.

John