Author Topic: HVAC Question: Dual Zone with Heat Pump.  (Read 3800 times)

BlueHouse

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HVAC Question: Dual Zone with Heat Pump.
« on: January 16, 2017, 08:14:23 AM »
Apologies if I use the wrong terms for my descriptions.  I’ve been googling and learning just enough to throw more words around than I knew yesterday. 

I have a 4-story row house with two heating systems in two zones.

Zone 1:  The first is an electric-powered heating/air unit (forced hot air) that heats/cools the first 2 floors of the home. This system is located in semi-conditioned space on Floor1.

Zone 2:  The second system is a heat pump that controls the temperature on the 3rd and 4th floors.  This system is located in conditioned space on Floor 4. 

I’m trying to find the best programmable settings for efficiency and comfort in the house.  It has recently come to my attention that I may have had the settings programmed so that the two zones/systems are actually competing against each other.  So I’ve been experimenting, and measuring temps at different times of the day, and what I’ve realized is that Zone2 rarely puts out “Warm” (>70 degree F) air (although sometimes it puts out 85degree, so I know it’s not broken).   It also seems to run a lot more than the Zone1 heater. 

Goal :  At 6am, I would like a warmish bed/bathroom on Floor3.  I recently changed the settings so that Zone 1 would turn on heat to 68 at 5:45am, in an attempt to create enough warm air in zone 1 so that by the time zone2 kicks on at 6am, there would be some warm air and I wouldn’t create cold drafts when zone 2 comes online.  But the air coming out of the vents on Floor 3 is about 67 degrees.  Outdoor temp is 35 and indoor temp at that time might be between 59-64.  So 67 will eventually heat the upstairs, but it sure feels cold on my shoulders in the morning! 

Is there an order in which I should try to heat the house so that the heat pump doesn’t have to work as hard and so that the air actually feels warm as it’s coming out of the vents? 

Any advice is appreciated and I am willing to do quite a bit of experimenting. 

BlueHouse

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Re: HVAC Question: Dual Zone with Heat Pump.
« Reply #1 on: January 17, 2017, 07:04:15 PM »
Anyone?  Bueller?

Papa bear

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Re: HVAC Question: Dual Zone with Heat Pump.
« Reply #2 on: January 17, 2017, 07:42:50 PM »
From my experience about heat pumps, they only raise the temperature of the air coming from the duct work a few degrees over the ambient air. Here in Ohio in an all electric neighborhood (stupid, and finally now have gas run) we would joke about the wind chill effect coming from the vents.  Gas forced air heat feels so much better and is significantly cheaper here.

I can't help with anything else here, but will act as a bump.


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Ocinfo

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Re: HVAC Question: Dual Zone with Heat Pump.
« Reply #3 on: January 17, 2017, 08:01:42 PM »
Regarding the heat pump, need to check if the emergency or auxiliary heat is kicking on. This is usually several electric coils that are 10-15kW and are basically like running 10 electric space heaters all at once. When these turn on, the output temp will feel warm but it's not very efficient. It's also possible that you have gas emergency heat, which is basically a just a regular forced air furnace so not too bad efficiency wise. I have an all electric condo with a heat pump and electric emergency heat. I've been told that with a heat pump, it doesn't make sense to let the temp drop well below normal as that causes the electric emergency heat to come on and basically negates the benefits of having a heat pump.


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Syonyk

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Re: HVAC Question: Dual Zone with Heat Pump.
« Reply #4 on: January 17, 2017, 08:18:18 PM »
Zone 1:  The first is an electric-powered heating/air unit (forced hot air) that heats/cools the first 2 floors of the home. This system is located in semi-conditioned space on Floor1.

Zone 2:  The second system is a heat pump that controls the temperature on the 3rd and 4th floors.  This system is located in conditioned space on Floor 4.

Find out a bit more about the Zone 1 system if you can - if it's a heat pump, great.  If it's just resistive coils ("electric furnace"), it's going to be painfully expensive to run.  Heat pumps are significantly more efficient.

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It has recently come to my attention that I may have had the settings programmed so that the two zones/systems are actually competing against each other.

Unless one of them is actually switching to air conditioning, there's no way they'll "compete" - the options, in heating mode, are "heat" or "don't heat."  Competing against each other would be, "One is heating, one is cooling."

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So I’ve been experimenting, and measuring temps at different times of the day, and what I’ve realized is that Zone2 rarely puts out “Warm” (>70 degree F) air (although sometimes it puts out 85degree, so I know it’s not broken).   It also seems to run a lot more than the Zone1 heater.

The "slightly warmer than ambient" air is how heat pumps work.  When the higher temperature is coming out, it's likely using the backup coils, which are really expensive (they're just big resistors, like your first story heater).

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Goal :  At 6am, I would like a warmish bed/bathroom on Floor3.

A small electric oil filled heater in the bathroom will probably be easier here...

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So 67 will eventually heat the upstairs, but it sure feels cold on my shoulders in the morning!

Heat it before you wake up and turn it off when you get out of bed.

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Is there an order in which I should try to heat the house so that the heat pump doesn’t have to work as hard and so that the air actually feels warm as it’s coming out of the vents?

You want to use the heat pump whenever you can, in terms of heating cost - they're radically more efficient than an electric furnace.  They just won't get "hot" air out of the vents unless you switch the backup coils on.  I suppose if you didn't care about cost and wanted warm air, you could run the heat pump with the backup coils (details of how to do this are up to your thermostat) and get quite warm air coming out.

I've been told that with a heat pump, it doesn't make sense to let the temp drop well below normal as that causes the electric emergency heat to come on and basically negates the benefits of having a heat pump.

That's true because the default thermostats installed with heat pumps are stupid.  If they see more than a few degree difference between "set" and "actual," they'll panic, turn the backup coils on, and try to make the difference up as quickly as possible.  This is idiotic from a cost of heating perspective.

If you have a not-stupid thermostat, you can tell it when you want things warmed up and it'll do what it can with the heat pump before using the backup coils.  I have a Nest, and it will often start heating at 4AM to have things up to the desired temperature by 7AM.  On a warmer night, it'll start later.  It uses the emergency coils on occasion, but not terribly regularly, and I'm reasonably certain it will have paid for itself with electricity savings this winter.

warmastoast

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Re: HVAC Question: Dual Zone with Heat Pump.
« Reply #5 on: January 22, 2017, 06:32:32 PM »
I also have a 2 zone, 2 unit heating/cooling system.  In a 2 story house.  Like you, the older unit downstairs is an air con unit that heats using heat strips.  This is eye-wateringly expensive.  The upstairs unit is a new heat pump with a nest thermostat.  When it was in full "smart" mode, the nest kept turning on the auxiliary heat strips,  it was turning it on at 2 or 3 am for a 7.00am set point of 68F.  So, I went to a subreddit for nest and learned that the heat pump should warm the house even with an outside temp of 25F and not need the heat strips.  Now, I live in Austin Tx and in the last few weeks we did actually have temps a tad lower than this overnight and daytime temps hovering around 32F.  So, I followed the instructions and turned off the heat strips completely to see how it would go.  No problem.  The heat pump managed to keep the house at 68F even though it was running a lot, it was way, way cheaper than having those aux strips coming on.  In the morning when the downstairs heating came on you can see the electricity consumption jumping right up so I keep that to a minimum.

If I lived somewhere colder, I might set the heat strips to come on at say 30F if needed. 

BlueHouse

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Re: HVAC Question: Dual Zone with Heat Pump.
« Reply #6 on: January 26, 2017, 02:06:23 PM »
Thank you all.  I thought this topic was dead.  I'll go home and check out the emergency heat options to see if that is occurring.  And maybe I'll set the program so that the heat pump does more heating/blowing while I'm downstairs or in bed rather than when I'm in the bathroom.

I suspect I may be getting the emergency heat thing happening...on some of the colder nights, I can hear something turn on for 30 seconds to 1 minute, then off again, then repeat maybe 20 times an hour or more before the heat is set to turn up.  I'm pretty sure the noise is coming from the heat pump, but I've been too cold to get out of bed and look.  I'll check tomorrow.

Thank you!