Question about 2 stage AC/Heat Pump


I just moved into a new house with an Amana 2 stage AC/Heat Pump. It is controlled by a Honeywell HZ432 multi-zone controller. For AC it 1st kicks in on stage 1 and if the temperature is not satisfied in 10 minutes (selectable on the HZ432), the 2nd stage will kick in. This is especially good as I am in an area where the temperature doesn't usually get real high in the summer (western NC mountains) which will allow unit will run a bit longer to remove more humidity. Now that it's heat pump season, the same 10 minutes applies to the heat pump. In my way of thinking, I would like to see the heat pump go directly to stage 2 so you can get as much heat as possible. I have heard here, many people complain about heat pumps and the drafty feel, etc., however, in this house, the HVAC guy got is right as I don't notice these problems. BTW, previously I've had a gas furnace for many, many years so I do know how that feels. Am I thinking wrong here? What are your opinions? Thanks.
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Art Todesco wrote:

'Pends on how you feel about economy vs faster response. There _may_ be a way to change the operation to control on dT instead of/in addition to simply time difference; the two-stage control on the geothermal system we had did that; it was Water Furnace-supplied w/ the pump; I don't know who actually built it.
You'll want to be sure to know whether that also is kicking in your backup resistance heat as well, of course.
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dpb wrote:

Thanks for the info. Actually, I wonder about economy? Running on stage 2 will, of course use more power, however, it will get the heat delivered faster and with less blower run time. The backup heat is actually a 2 stage propane furnace (Goodman). So far this season, it has only come on during one cold morning and I think it came on because the outside coil was deicing.
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Art Todesco wrote:

I doubt the time will be sufficiently reduced to be observable on energy savings. I'd expect the added load to more than compensate while running at the second stage. Remember, it's a fixed dH to raise the temperature a specific amount irrespective of time. You'd have to have actual performance figures to know how linear the power cost is vs heat output at the two performance levels to get a computed estimate. Other than that, it would take monitoring usage each way over a significant time such that day-to-day variability would average out.
BTW, in marginal area, might want to consider an interlock on the backup heat so it only comes on below (say) 20F or somesuch. Did that w/ the geothermal system in E TN by adding an external thermocouple into the control loop calling for the backup. W/ the geothermal (rather than air-exchange) it made it essentially a non-starter that was almost never needed. Air-exchange are much improved since the one that system replaced, but am sure it would still have come on more often w/ a newer one than w/ the ground source but wouldn't have been just a cool-morning thing.
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says...

Whatever rings your chimes. If you find a big blast of heat satisfying, it's your house and your electric bill. The most efficient heating system is one that never shuts down or cools off. A lower powered heat pump will also create less hot and cold spots in the house. The second stage is there for colder days when the smaller heat pump just won't do the job. If you want to set the heat pump to go directly to stage 2, you will pay a few extra bucks for heat, but other than that I don't see it will do any harm.
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wrote:

Am I the only one wondering what sense it makes for the heat pump to always start on stage 1 for 10 mins, then move to stage 2? It would seem in any properly sized system, 10 mins of AC run time would rarely be enough to cool the house even 1 degree. And in any case, it would seem the thermostat would be smart enough to have a better way of figuring out what stage to start at, eg the current temp delta, how hot it is etc. Seems strange to waste 10 mins on stage 1 if the house is 85.
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snipped-for-privacy@optonline.net wrote: ...

I was _presuming_ (dangerous, I know... :) ) that there's more to the control logic than simply time but wasn't interested enough to either try to look up the thermostat datasheet or ask the OP... :)
I think this is one of those that has a "self-learning" mode that is based on several inputs the demand dT being only one and they also use previous heating/cooling "histories" to try to find a site-specific strategy. How well they'll work in practice will be dependent on just how clever the programming was and the suitability to the particular installation.
I've never actually had one; only read about some of the logic designs in a few of the engineering trade magazines. My general impression has been they seemed too gimmicky to be of much real value in comparison to more simple control schemes w/ setback so that I really wondered if they could demonstrate any actual advantage to speak of or whether were more marketing/feature-rich driven.
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dpb wrote:

Well, it is based only on time, when the HZ432 is being used to control the heat pump or AC. You can set it from a few minutes to, I think, 15 or 20. I agree that I can't see "wasting" 10 minutes waiting for heat and then go to stage 2. I think the thermostat has multiple stages of heat, but it is only 3 stages and I have 4. I am thinking that it the whole thing would be better controlled by the thermostat than the HZ432. I have looked at various thermostats that have seem to do a better job of detecting when to bump up to the next stage. I think my next thing to do will to call Amana/Goodman and also Honeywell. I hate calling Honeywell because you get a call center in Asia.
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We sell Amana and have installed a number of two stage HP's. We typically use a White Rogers stat, though I can't tell you the model off the top of my head and don't feel inclined to go check right now. Anyhow, I have often thought about exactly the same thing. The WR stat does "learn" cycle times and how long t takes to sense any temp change when it decides to kick stage two in. On Amana two stage you drop about 1/3 capacity in low stage. It would be easy enough to rig a HP to only run in high on heating. I have brought up the idea, but we have never had any customer complaints, so never tried it. Anyway, all you would have to do is have a relay that is powered from the 'Blue" wire on the stat (which powers in heat mode and is usually only used with Rheem/Ruud HP's) Just have that relay jump Y1 and Y2 togther when it is powered , which is only in heat. BTW, I have toyed with the idea of putting a 16 SEER two stage Amana 3 ton HP in my house, but as long as the antique Trane keeps on going I probaby will never do it. (Waiting for the distributor to get one dinged up with only cosmetic damage that they will make a deal on (: Larry
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