Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

HZ432 - Heat pump + hydro (oil) 'dual fuel': Zone panel Settings Question

New installation, working well but not behaving as I expected.

I'm trying to find out if I misunderstand the manuals, the settings are wrong or there is somehow a faulty control board? The manuals are very sparse, and the Helpdesk is nonexistent for consumers.

It's a bit complicated setup, let me paint the picture first:
  • My regular heating company has just installed a new heat pump (Trane XR), hydro air handler (first co. VHBXB-HW), controlled with a new Honeywell HZ432, and hooked up to my oil boiler (Energy Kinetics EK2).
  • The HZ432 is set to 'dual fuel'. Wiring seems to be conform diagram for this too. So Y controls the heat pump (plus O for cooling), and W controls the 'backup heat'.
  • 4 Zones with Honeywell thermostat (TH6210U), and outdoor temperature sensor connected to zone panel. If outdoor temp too low for heat pump, panel switches to backup heat.
  • The VHBXB-HW has a variable 'smart' fan that is programmed to delay start, ramp up slowly, and do a gentle purge afterwards to get rid of residual heat (and cold, I guess).
Slow ramp up and slow purge afterwards work fine in heat pump mode.
But in fossil fuel mode it doesn't want to work that way.

In 'Fossil Fuel mode' , W gets energized together with the fan (G) and the AHU fan start straightaway. After the call is satisfied, the boiler stops and the fan stops straightaway too. No ramp up, no purge!?

Question I have now is why don't I get delayed start and purge with 'backup' heat? It's not too bad now but this is going to be uncomfortable in winter!

a) Should G be energized at all along with W? The AHU manual shows only W is supposed to be energized for 'hydro/oil' heat.

In the HZ432 settings I've checked 'control of fan in heating' is set to HVAC (as opposed to HZ432) in its setup, so unclear why G gets energized at all. This 'HVAC controls fan in heat mode' doesn't seem to change any behavior.

What effect should this setting have?

b) If G gets energized along with W, could that throw the air handler off and make it skip slow ramp up and after purge?

c) How would this ever work if I, say, had baseboard heating as 'backup heat', not hydro coil? In that case the baseboard heating would come on along with a fan blowing cold air?

I have a suspicion this 'Dual Fuel' mode of the HZ432 is only meant to be used with electric backup heat, for when the heat pump can't make it. Or there is a subtle configuration issue, because the manual mentions 'fossil' as a backup source, so this has got to be possible too.

Is there anybody who has a similar setup - an HZ432 panel with HP and oil backup? Do you see the same behavior?


Thanks in advance!

Waldo



Comments

  • Robert O'Brien
    Robert O'Brien Member Posts: 3,451
    EK typically uses the end switch of zone valve to activate the blower, keeping the fan operating whenever the zone valve is open thus enabling purge.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    SuperTech
  • wvriem
    wvriem Member Posts: 27
    Hi Robert,

    Thanks for the reply - but my setup seems to rely on a timer, there's no link back from the zone valve to the air handler. Good solution especially when the boiler is prioritizing hot water. But unfortunately not easy to add in my setup due to distance..

  • Robert O'Brien
    Robert O'Brien Member Posts: 3,451
    Was it hydroair previously?
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Hot_water_fan
    Hot_water_fan Member Posts: 521
    What's your heat loss and what's the heat pump's output at design temp?
  • wvriem
    wvriem Member Posts: 27
    Was it hydroair previously?
    Yes - it was a single speed air handler, with ac only coil. Heat output on hydronic is the same as the old setup, just adds the option for heat pump + variable speed fans.

    Heat output max is the same as the old hydro coil. HP added to be used in mild seasons only.

  • Ironman
    Ironman Member Posts: 6,868
    The issue is probably that because the 6210 stat is configured for heat pump operation that it’s sending power to “G” when there’s a call for heating or cooling. The HZ432 then transfers that to the AHU.

    You may have to add a relay at the AHU that breaks “G” when “W” is energized.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Hot_water_fan
    Hot_water_fan Member Posts: 521
    Heat output max is the same as the old hydro coil. HP added to be used in mild seasons only. 
    Mostly likely dramatically oversized, which is okay. There’s a chance the heat pump can cover the load all of the time (much cheaper than oil), which is why I asked. You can give it a try using last years fuel ups:
    https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
    wvriem
  • wvriem
    wvriem Member Posts: 27
    Ironman said:

    The issue is probably that because the 6210 stat is configured for heat pump operation that it’s sending power to “G” when there’s a call for heating or cooling. The HZ432 then transfers that to the AHU.

    You may have to add a relay at the AHU that breaks “G” when “W” is energized.

    That could be it. It should be possible to use the HZ432 with 'dumb' thermostats, so I could test and configure the 6210's to behave like classic thermostats? It says so in the manual for the HZ432 but there's no information if this would require different wiring.

    In other words, if I "dumb down" the thermostat, would the HZ432 then make the decision to 'translate' a W call for heat to the heat pump, depending on the outdoor temperature sensor? Documentation on the exact behavior of this HZ432 is rather lacking...

  • wvriem
    wvriem Member Posts: 27

    Heat output max is the same as the old hydro coil. HP added to be used in mild seasons only. 
    Mostly likely dramatically oversized, which is okay. There’s a chance the heat pump can cover the load all of the time (much cheaper than oil), which is why I asked. You can give it a try using last years fuel ups:
    https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
    That was an interesting link, thanks! Got some oil delivery records so I can compare actual usage for, say, Feb last year. Roughy doing the math it looks like the oil boiler is about 60% oversized, but the heat pump alone would be undersized - which is roughly what I was going for: use the heat pump in the milder days and fall back to oil heat if it gets really cold.

    Hot_water_fan
  • Ironman
    Ironman Member Posts: 6,868
    edited November 2021
    wvriem said:
    The issue is probably that because the 6210 stat is configured for heat pump operation that it’s sending power to “G” when there’s a call for heating or cooling. The HZ432 then transfers that to the AHU.

    You may have to add a relay at the AHU that breaks “G” when “W” is energized.
    That could be it. It should be possible to use the HZ432 with 'dumb' thermostats, so I could test and configure the 6210's to behave like classic thermostats? It says so in the manual for the HZ432 but there's no information if this would require different wiring. In other words, if I "dumb down" the thermostat, would the HZ432 then make the decision to 'translate' a W call for heat to the heat pump, depending on the outdoor temperature sensor? Documentation on the exact behavior of this HZ432 is rather lacking...
    No, the stat has to be configured for heat pump because the “Y” terminal has to energize the compressor contactor for BOTH cooling and heating.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    wvriem