Dual Fuel, 2 Stage, 2 Zone System


Old 03-11-17, 08:59 AM
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Dual Fuel, 2 Stage, 2 Zone System

Hi All,

Sorry for the long winded post, but I felt the more details the clearer the situation.
My daughter is having a new home built in Southern Delaware and I am having the builder install the following;
Goodman GMVC96060 2 stage propane furnace
Goodman DSZC16036 2 stage heat pump
HZ432 zone controller for 2 zones with outside temp sensor.
I think I need a T6 series TH6320U thermostat (she likes the look of the T6)
Air flow through the system is [filters]->[A coil]->[furnace]->[zone dampers]
There is a barometric bypass on the system

The house is about 2400 ft^2, with a first floor zone 1 about 1900 Ft^2 and second level Zone 2 about 500 Ft^2. Zone 2 is semi-open to the lower area through a balcony and open stairs. I am very concerned about summertime humidity, thus the reason for the 2 stage Heatpump. And the 2 stage gas is for efficiency so that the system can maximize run times and efficiency.

Fuel for the furnace is propane at about $2.50 Gal and electric is $0.12/KW.

I have done a bunch of poking around to see the best way to configure this system to operate like I think it should and would like to confirm what I found.

The way I would think it should operate is as follows....
Cooling: Zone 1 stage the compressor based on Delta T setpoint to room. Zone 2 only allow first stage as a second stage will be a lot of bypass. Both Zones: Delta T zone 1
Heating: Zone 1 stage based on Delta T . Zone 2 I stage only, Both Zones based on Delta T Zone 1. Below Balance Point, which looks like 25* from the manual J, Gas furnace staging same as HeatPump staging.
Emergency Heat: I staging don’t know but probably the upstage timer in the furnace?
Based on that, I assume the HZ432 is wired as a 3H/2C heatpump ( so I get Aux and Emergency heat functions ) and the T6 TH6320U2003 is connected as a 3H/2C system also.
The critical parameters in the thermostat:
200= Heatpump
205= air-air
220= 2 stage
221= 1 Aux
253= ??? Probably “ether”
255,256 Gas
260= Ext Fossil Fuel kit
360= Aux drop??? I don’t know

For the HZ432:
Set Balance point in advanced menu to 25*
Dual Fuel, 2 Compressor Stages, 2 Dual Fuel Heat,
Zone 1 T/S=HeatPump, Stage 2=Thermostat, Stage 3=??? ( no? ) Or can 1 stage of gas be on with heat pump?
Zone 2 T/S=HeatPump, Stage 2 Off. ( or a % of zones??)

Questions: Will there really be a Stage 3 available on Zone 1?
If Zone 2 Stage 2 is ‘off’, will it allow Stage 2 to come on based on Zone 1?
Is there a better way to configure this?

Thanks, Tim
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Old 03-11-17, 09:24 AM
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Welcome to the forums.

A lot there to digest. My forum partner, Houston, could answer this one better than I can.

One question..... had you looked into two units as opposed to duct zoning ?
Furnace/heatpump for first floor. Heat pump only for second floor.
Old 03-11-17, 11:22 AM
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Thanks for the prompt response!

Two units was my original idea but the builder, a very large company, said they do not support this as their standard practice and the zoned system would work well.

I did some work with them to get a 2 stage heat/cool heat pump and 2 stage gas furnace. Typically they drop a single stage furnace and single stage A/C. Yikes! :NO NO NO: Since the top area is fairly open to the lower area and the return air grills are on all levels, it may have a shot at working. We will see.
Old 03-11-17, 11:22 AM
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Have you asked the builder to put you in touch with his HVAC sub to discuss this? Too many times detailed specs get lost. All of your planning could be for naught if the ductwork is inadequate (like most are).

For air flow the coil should be after the furnace to keep the heat exchanger from rusting out.

A 3 ton unit in first stage will operate like a 2.2 ton unit. That is way oversized for cooling a 500 sqft 2nd floor even with a bypass. I like Pjmax's suggestion of a separate system.
Old 03-11-17, 01:12 PM
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Yes, 2 systems would be ideal, however that is not in the cards. So I need to make this work with the HVAC sub's help. Ductwork seems like it is pretty decently sized to second floor for 700CFM, should be about 800Ft/Min. That is why I want to limit Zone 2 to first stage only. There is a 12" round supply with 2-6", a 7" and a 5" takeoff.

Actually the DSZC16036 will operate at 2T on first stage. I plan to have them leave the Zone 1 dampers open a crack if there is too much bypass and the DATS trips. My logic is: If Zone 2 needs cooling, then Zone 1 probably could use some also.
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