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Old 04-02-2010, 03:47 PM   #1
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


We have a Honeywell VisionPro TH8320 thermostat that is controlling an FHP WD-300 geothermal heat pump unit (hereafter called “the unit”). The unit is fitted with the FHP 641-065 SX interface board. Current pertinent connections are... TStat to the unit / board ... R to R, OB to O, G to G, Y to Y1 (via a relay), Y2 to Y2 (via a relay).

We have recently built a solar system. One of the solar heat exchangers loops through a radiator which is mounted in the heat pump’s air flow to warm the air coming out of the blower. So... we want to install a 24VAC relay which will turn on the pump for this radiator loop. We want the first stage of heat control from the thermostat to do 2 things only... 1) turn on this radiator relay and 2) turn on the blower fan. So our proposal to accomplish this is to connect the Tstat OB terminal to the new radiator relay. We also thought of connecting this same OB terminal to W1 on the FHP board so that the blower will be told to come on when the radiator pump comes on. However, we’re afraid that connecting it to the W1 terminal might also cause the compressor to run which we do NOT want to happen in stage 1.

Then, for stage 2 we want the unit to operate the way it does currently. For that we thought of connecting AUX to O. OK... the O terminal on the FHP board expects a signal to actuate the reversing valve. Will AUX do that?

Of course this is for heating only. We want the cooling to operate normally in the summertime.

Maybe I’ve made this too complicated. Bottom line... what should we do to accomplish our goal.

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Old 04-02-2010, 05:09 PM   #2
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


Won't work the way you want to wire it.

First. on your unit, O/B should be energized in cooling mode(I could be wrong on that, check your stat's installer set up to see how its set).
Next, W1 and W2 are aux heat. Not heat pump heat.

Your thermostat energizes Y1, and G on a call for first stage heat.
Then it energizes Y2 if the temp drops.

I have no idea why you have relays controlling Y1 and Y2?

Currently. No thermostat is made to use another source as stage 1 before using the heat pump.
If your heat pump wasn't 2 stage. it would be easy to do.

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Old 04-05-2010, 08:16 AM   #3
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


The install manual says that the default setting is "O/B terminal controls valve in cooling" and ours is set that way.

I thought Y1 and Y2 were for cooling. Or is that only in conventional (not heat pump) mode? So with a heat pump, how do Y1 and Y2 function?

So, I hear you saying that it would be easy to connect the systems so that the solar system would kick in when the heat pump could not keep up with the need for heat and that to activate our solar system as the first provision of heat, and the heat pump kicks in when the solar cannot keep up... that there is no thermostat made that can do that. Right? What a pity.
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Old 04-05-2010, 05:20 PM   #4
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


Y1 always turns on a compressor, and Y2 either turns on another compressor, or engages second stage or a single compressor.
Its the O/B terminal that controls weather the outdoor unit is running in heat or cooling.

Since an air to air heat pump generally can't heat a house by its self at design temps. It need a back up heat source. So stats aren't designed to use them as an aux heat source for another source.
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Old 04-07-2010, 07:13 PM   #5
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


There are always several diff. ways to get something done. You can use your present combination to control the solar assist by adding a relay and a switch.

The relay contacts disable the Y and Y2 lines between the present thermostat and the FLHP. The switch selects either disable solar assist or solar assist.

The relay needs to have a 24 v. AC coil and two sets of contacts that are double pole double throw. Double pole means each relay switch arm can be resting on one contact or the other of two contacts. Picture two contacts with a bar between them. The bar will rest on one side or the other depending on wheather the relay is energized or not.

Double throw just means there are two sets of what is described above.

One set of contacts makes or breaks the Y1 line between the thermostat and the FHP. The other set of contacts makes or breaks the Y2 line to the heat pump. One side of the relay coil uses a wire from the common screw of the thermostat (now there are two wires on this screw). The other side of the relay coil need a wire from the R screw (now two wires on the R screw) and gets interupted by an on off switch. The R should measure 24 v all the time from the system transformer that runs the thermostat. So when the switch is in one position the relay coil is energised and in the other switch position the coil is off. I do realize that we are not using the other side of the relay contacts but a double pole double throw relay is more common and generaly cheaper on the surplus market. The current rating of the contacts is no isssue because the switched current is tiny.

Now you should have manual control of which system - solar or heat pump is active and the heat pump's fan will run for solar heat if the switch is set for solar. If you want contacts to run a solar pump then the relay needs another pair of contacts for the pump (and rated for the pump current).

If it was mine, I would add another item. There needs to be an adjustable temperature switch that is driven by the solar water temperature. If the water temperature is above a minimum - say 90 degrees - the switch contacts are closed. These contacts would go in series with the relay coil so that only if the solar water is warm enough to use - the relay would be energized and allow solar heat and disable the Heat Pump until the water is depleated of heat and the relay denergises - allowing the heat pump to take over without the solar pump running.

Clear?

There are some other tricks that could be used since the fan motor is variable but that another issue.

I've just finished a *****ing job with a new FHP that has kicked my ass around the block.

John
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Old 04-09-2010, 09:58 AM   #6
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


grifzila/John,
That's a very interesting idea you present there. I like it. I think that's just what I need

A key phrase you have in there is ...

"and the heat pump's fan will run for solar heat if the switch is set for solar."

That's a point I wasn't clear about. I understand you to imply that the fan will run at high speed even though the Y and Y2 terminals are disabled. Is that right? That's critical for this to work.
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Old 04-09-2010, 03:21 PM   #7
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


I type in a detailed response to your comment only to have it disapear - I'm not willing to retype it. There is some info that you need - send me an email tm_jy@hotmail .com and I'll phone you with the details.

John

That address is tm jy - the editor always underlines it all.
underscore
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Old 04-28-2010, 09:21 AM   #8
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


John, I have built the circuit you described in your post of 4/7 and works great. I had thought I needed more than the slowest fan speed, but at this point I believe that for my purposes the 1200 CFM I am getting is adequate to transfer the heat I am bringing into my solar storage tank into the room in a reasonable amount of time.

I used your idea of a thermal switch, but that has not proven to be as slick as I'd at first thought. I acquired quite cheaply from Ebay an ApCom WH10A upper thermostat for a double element hot water tank. This is a double throw switch which is necessary because I am using this in the opposite fashion than per it's designed intention. When used on a hot water tank, a low temperature closes a circuit to activate an electric heating element. In my case I want a low temperature to DEactivate my relay circuit because that means that there is not enough heat in the solar tank to help warm the room air.

But there is at least one practical problem with this,
I mounted the switch onto the pipe which supplies water to my solar panels, assuming that that would give a reasonable indication of tank water temperature, which it would IF I am circulating water to the solar panels. But that is not happening at night or early morning and yet, I want to be able to draw heat from the tank to the room at those times. So I might need to figure out a different way to subject the thermal switch to the solar tank water temperature. I tried attaching it to the heat exchanger exit pipe, hoping that even if there is no circulation in that loop, that tank temperature would reach the switch via conduction of the pipe material, but that doesn't seem adequate.

Also, I had thought that I needed for the switch to turn on at lower than its about 110°F (it's adjustable and it claims its low end to be 90°F, but doesn't seem to be that low in practice) but I'm finding that the solar water needs to be at least that warm to be able to make a significant difference in the room temperature. I'd better just let the geothermal heat pump take over if I don't have that much.

Well, that's my contribution for now.
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Old 04-28-2010, 02:55 PM   #9
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


If you can find a more appropriate place to mount the tank sensor, the switch you have can be rigged to a different range. The guts consist of a bimetal disc that snaps inside out at a certain temperature if tightly coupled against a heated surface. Usually they can be modified by removing the pointer stop pin to allow a slightly diff. pressure on the disc. screw. I have found it is more important to clamp the switch tightly to the surface, cover with insulation so the air doesn't cool the case, and use thermal grease between the surfaces of the tank and switch. If you don't have a good heat sink grease, zinc oxide paste in a tube for sun protection works fine - don't be stingy with the amount of grease. Radio Shack sells a low grade silicone heat sink grease but it is a tiny tube and not the best choice.

There are plenty of other choices for the temperature control. Look in the hobby field for kits, or surplus mechanical ones or electronic ones that can drive a relay coil. I've even used standard old mechanical house thermostats from the trash pile that have a glass and mercury tube with contacts in each end. To get it to run in the range you need ^< 125 degrees F, you will have to screw with the stops and rotate the base to get the glass tube to be near horizontal at the range you need. Again, it has to be isolated/insulated away from interfereing room air. Simple is almost always best.
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Old 04-28-2010, 04:00 PM   #10
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


I had opened up the switch and I could see something of the action involved in raising the threshold temperature, but I didn't see a way to make the lowest temperature point lower still. But I think you are referring to the outside. My pointer comes against some arc-shaped raised plastic. I could either cut that away or remove the pointer on the knob so it could continue to be turned more counterclockwise past the beginning of the plastic arc. Also I had already applied heat conductive grease and also insulated the pipe and the switch in that area.

As an alternative I am planning to build the circuit Craig suggests here...http://www.craig.copperleife.com/tech/thermo/
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Old 04-28-2010, 05:39 PM   #11
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Configure an add-on radiator as stage 1 heat using a Honeywell thermostat


Yes, I was refering to the outside pointer stop - some have a metal post others - some internal stop. The electronic switch you pointed to will give tighter resolution. Careful of the coil current unless using the transistor driven one.

Your on the right track.

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