Three stage cooling and Two stage heating.

[jjmarquez84]

I helped install a new residential multistage heat pump system that was equipped to provide three stages cooling with two stages of heating. To be honest I really don’t understand how all the stages of heating and cooling were to be accomplished by the t-stat. I guess it’s something that I never picked up, or really understood but what I don't understand clearly is how or what controls the stages? Any takers?

[motoguy128]

3 stages? How was that managed?

You might need one of those little PLC type programmable controllers with display that has analog inputs and at least 6 digital outputs.

[Txvman]

A digital t-stat with 5 relays could easly do it. Pretty easy really. Honeywell make 3H/3C t-stats. Not cheap thou.

http://customer.honeywell.com/honeywell/productinfo.aspx/T7350H1009

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[pacnw]

I do not understand how there would NOT be more stages of heat.

You should have the same heat and cool from heat pump(in theory) as well as at least 1 stage of back up, maybe more.

[Txvman]

Mind you this is a guess, 3 compressors and 2 reversing valves.

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[mark beiser]

What brand?

[motoguy128]

What brand?

I'm really curious on this. I'm having trouble seeing the value over something like a Carrier Greenspeed.

Maybe it's a two scroll unit with two refrigerant circuits and one of the scrolls unloads? But in heat, you only run with both loaded, since I think unloaded you don't gain any efficency in heating mode.

Or a custom air handler with a A coil that has 2 refrigerant circuits and one of them is a 2 stage condenser.

An interesting alternative when you think about it in applications where you want some redundancy and a sytem that rusn almost constantly or has a very small zone, but don't need more than 5 tons and are space limited to a single air handler. but it seems to me that an inverter unit would be better.

[jjmarquez84]

Your right looking at it agian its 3heat and 3 cooling.

[jjmarquez84]

Trane.Trane.

[54regcab]

Are you absolutely sure it isn't the much more common 2 cool/3 heat?

[billygoat22]

maybe controlling two units off one tstat? a/c units and furnaces?

I had a 3 cool, 2 heat a few yrs back. used a time delay for last stage.

[zacmobile]

This is quite common on geo systems and I would think on most air source HP's.
Generally you would have a two stage compressor with two stages of heat and two of cool & 1 back up. I'm pretty sure most t-stats i've used have a time delay or a combination of temperature change over time for the back up/3rd stage relay.

[motoguy128]

This is quite common on geo systems and I would think on most air source HP's.
Generally you would have a two stage compressor with two stages of heat and two of cool & 1 back up. I'm pretty sure most t-stats i've used have a time delay or a combination of temperature change over time for the back up/3rd stage relay.

But he's talking about 3 cool, 2 heat. The vision pro IAQ will do 4heat, 2 cool. But I haven't seen one that will do 3 cool, there's not much demand for it.