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Thread: Qs on my new system
11-21-2007, 02:04 PM #1Regular Guest
- Join Date
- Mar 2005
- Cary, NC
Qs on my new system
I have a few questions on the operation of my new HVAC system (replacement of old system). I am wanting to clarify my knowledge and cross-check what the installer will tell me once he returns my calls. He seems like a good guy, but as someone once said "trust but verify".
House is 2200 sq ft, 3 stories including a walk out basement which is 400 sq ft of low load. Located in central NC.
Equipment installed is a Trave XV80 80k btu plus a Trane XL16i heatpump. Three zones, one for each floor. System controlled by Honeywell TZ4. Tech explained that the system is set up such that the TZ4 will be the "brains" rather than the thermostats. Tstats are Honeywell VisionPro TH8000 series on main floor and Honeywell T8665A Chronotherm IV wireless on the second floor and basement.
Reading through the TZ4 zone board manual I can see the following
Wiring looks like it matches that for Dual fuel w/ 2-stage hp and 2 stage gas
Bank 4 dip switches set for "Timer Operation" on both hp and gas with 10 minutes of stage 1 run.
Bank 5 is set up as
5-1 = system type = hp
5-2 = DATs low limit = 48F
5-3 = purge mode timing = 2 minutes
5-4 = fan control during purge = HVAC controlled
5-5 = damper control during purge = last zone calling
5-6 = fan control during heat = panel control of fan in heat and cool
5-7 = Operation of O/B hp changeover equip terminal = O/B equip term energized in cool
5-8 = Dual fuel operation = enabled
Here are my Qs
1) Is this dual fuel setup a "fixed balance point" setup for heating?, i.e. hp runs until temp drops below zone board temp dial setting and then gas runs?
2) The board was set at about 38-40F changeover which is what this company recommended. However, reading posts here it seems the hp can run fine in the low 30s. Checking gas vs electric here, gas is $10/mo plus 1.34/therm and electric is $6.75/mo plus .087/kwh. When I plugged these into a online calculator, the hp was a better deal than gas until temps got very cold. Question is, if I set the hp to around 32F, will it do its defrost cycles ok, or does the above setup with the zoning board and dip switches interfer in some way?
3) When hp defrosts, will it be blowing cold air under this setup? How does the hp determine when to defrost?
4) Does gas ever kick in under this setup if Otemp is above changeover point? e.g. if Tstat is coming out of setback and needs to gain several degrees.
5) Is a DAT sensor necessary? There is not one hooked up for this system. Manual mentions DAT sensor is used to "control capacity and prevent high limit or coil icing".
6) Fan blows much stronger when gas is used vs hp. I was told this is because there needs to be a certain amount of airflow over the gas furnace heat exchanger to prevent it from becoming too hot.
7) What does dip switch 5-7 regarding "O/B equipment terminal energized in cool" mean?
8) At the bottom of the zone board there are the wiring connections for the 3 zones. Zone 1 (main floor) and zone 3 (basement) have red and blue wires connected at the far left, but zone 2 (2nd floor) does not. Thermostats as mentioned above.