Question about 2 stage AC/Heat Pump

Posted by on October 27, 2009, 10:28 am

wrote:

> says...

> > I just moved into a new house with an
> > Amana 2 stage AC/Heat Pump. =A0It is
> > controlled by a Honeywell HZ432
> > multi-zone controller. =A0For 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. =A0This 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. =A0Now that it's heat pump
> > season, the same 10 minutes applies to
> > the heat pump. =A0In 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. =A0I 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. =A0BTW, previously I've had a
> > gas furnace for many, many years so I do
> > know how that feels. =A0Am I thinking
> > wrong here? =A0What are your opinions?
> > Thanks.

> Whatever rings your chimes. =A0If you find a big blast of heat satisfying=

> it's your house and your electric bill. =A0The most efficient heating
> system is one that never shuts down or cools off. =A0A lower powered heat
> pump will also create less hot and cold spots in the house. =A0The second
> stage is there for colder days when the smaller heat pump just won't do
> the job. =A0If 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. =A0
> --
> For email, replace firstnamelastinitial
> with my first name and last initial.- Hide quoted text -
> - Show quoted text -

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.

Posted by dpb on October 27, 2009, 10:36 am

trader4@optonline.net 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.

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.

--

Posted by Art Todesco on October 27, 2009, 11:07 am

dpb wrote:

> trader4@optonline.net 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.

>
> 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.
>

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.

Posted by Lp1331 1p1331 on October 27, 2009, 9:26 pm

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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Question about 2 stage AC/Heat Pump - Page 2