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HVAC/Heat Pump Question

 
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Old 12-05-2018, 12:57 AM   #1
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HVAC/Heat Pump Question


Being from the northeast I am very familiar with natural gas/propane/oil fired boilers and furnaces.

Now that I have moved to the PNW I have a question. Bought a place out here and had a new heat pump installed as the house lacked AC.

With the cooler temperatures a thought occurred to me regarding thermostat setback temperatures. My entire life I have been a proponent of nightime, and daytime, set back temperatures on a thermostat. Just for example if between 10pm and 5am the temp setting is 60, and 70 all other times. Of course it helped on my projects to be building very efficient insulation systems (SIP's) wrapping a substantial thermal mass Timber Frame

Recently a HVAC tech told me that if the thermostat setting is more than 2 degrees differential that the "backup" electric coils kick in with a heat pump. If this is true, would it not be more efficient to keep the same setting all the time so that the heat pump can maintain the setting without the coils kicking in?

Inquiring minds and all that. Thanks. I know that varying insulation and building design will effect all of this. As well as energy costs, system efficiency, degree days... and on and on. Just wondering what your sense is on this.
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Old 12-05-2018, 01:09 AM   #2
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Re: HVAC/Heat Pump Question


i'm in grants pass and in the winter months we have found it most economical to set it & forget it.

in the cold weather it takes too long for the air source heat pump to get to temp.

winter we set temp to 68-70 deg and leave it alone.

experimented several times with dropping temp to 64 at night and it just did not work out.

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Old 12-05-2018, 08:38 AM   #3
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Re: HVAC/Heat Pump Question


Quote:
Originally Posted by archtimb View Post
Being from the northeast I am very familiar with natural gas/propane/oil fired boilers and furnaces.

Now that I have moved to the PNW I have a question. Bought a place out here and had a new heat pump installed as the house lacked AC.

With the cooler temperatures a thought occurred to me regarding thermostat setback temperatures. My entire life I have been a proponent of nightime, and daytime, set back temperatures on a thermostat. Just for example if between 10pm and 5am the temp setting is 60, and 70 all other times. Of course it helped on my projects to be building very efficient insulation systems (SIP's) wrapping a substantial thermal mass Timber Frame

Recently a HVAC tech told me that if the thermostat setting is more than 2 degrees differential that the "backup" electric coils kick in with a heat pump. If this is true, would it not be more efficient to keep the same setting all the time so that the heat pump can maintain the setting without the coils kicking in?

Inquiring minds and all that. Thanks. I know that varying insulation and building design will effect all of this. As well as energy costs, system efficiency, degree days... and on and on. Just wondering what your sense is on this.
You can adjust the delta and time delay for aux heat.
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Old 12-05-2018, 02:41 PM   #4
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Re: HVAC/Heat Pump Question


Yes, adjust delta for mild weather. But when it gets too cold outside, the efficiency curve will shift to aux heat (compressor running too long for little heat generated so switch to aux)
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Old 12-05-2018, 03:07 PM   #5
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Re: HVAC/Heat Pump Question


Quote:
Originally Posted by griz View Post
i'm in grants pass and in the winter months we have found it most economical to set it & forget it.

in the cold weather it takes too long for the air source heat pump to get to temp.

winter we set temp to 68-70 deg and leave it alone.

experimented several times with dropping temp to 64 at night and it just did not work out.
have found same results here. doesn't save to turn off the heat at night because in morning it runs for an hour till back to temp up.
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Old 12-05-2018, 08:13 PM   #6
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Re: HVAC/Heat Pump Question


I've been through 3 different brands of top of the line variable speed heat pumps in the past 2 years. One of them I couldn't raise the temp even 1 degree without the backup heat coming on, absolutely dumb.

With that said it's best to set and forget, I might set mine up only 1 degree.

With my present system I have the low balance point set to use heat pump down to zero.
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Old 12-05-2018, 09:20 PM   #7
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Re: HVAC/Heat Pump Question


Even without backup heat on, they are less efficient when running at higher output levels, assuming it's a modulating mini split style.
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Old 12-05-2018, 09:28 PM   #8
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Re: HVAC/Heat Pump Question


Long term, a L.P. fuel back up heater would save $$ during cold snaps? And have several times the Btus of any 50-60Amp x 240 Vac heater element.....

Any chance of setting the coil in running water, a small creek would provide several houses with night time heat....

Perversely, setting your thermostat higher while your at work, might allow you to store the "cheaper" heat output of 12-4 degree warmer daytime air...
Maybe in a water tank or masonry trombe wall/floor, or even a few ceiling fans blowing on a concrete slab on grade.

Build Nuke plant on the coast for cheap power 24-7?

damn up one of the many rivers return billions of KWatts of gravitational energy of falling water...... Nearly FREE Power for 100s of years......

Or, Do the Jimmy Carter and buy more sweaters....

This is a First World self inflicted problem, IMHO, irrational Eco-Nutter public policies = over priced electrical power.
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Last edited by Fouthgeneration; 12-05-2018 at 09:31 PM.
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Old 12-06-2018, 04:22 AM   #9
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Re: HVAC/Heat Pump Question


Quote:
Originally Posted by archtimb View Post
Being from the northeast I am very familiar with natural gas/propane/oil fired boilers and furnaces.

Now that I have moved to the PNW I have a question. Bought a place out here and had a new heat pump installed as the house lacked AC.

With the cooler temperatures a thought occurred to me regarding thermostat setback temperatures. My entire life I have been a proponent of nightime, and daytime, set back temperatures on a thermostat. Just for example if between 10pm and 5am the temp setting is 60, and 70 all other times. Of course it helped on my projects to be building very efficient insulation systems (SIP's) wrapping a substantial thermal mass Timber Frame

Recently a HVAC tech told me that if the thermostat setting is more than 2 degrees differential that the "backup" electric coils kick in with a heat pump. If this is true, would it not be more efficient to keep the same setting all the time so that the heat pump can maintain the setting without the coils kicking in?

Inquiring minds and all that. Thanks. I know that varying insulation and building design will effect all of this. As well as energy costs, system efficiency, degree days... and on and on. Just wondering what your sense is on this.
Best to set it to 1 temp, and leave it set there.

Even using a thermostat that can lock out the aux heat until the outdoor temp drops to X degrees, has the same problem. Once the outdoor temp drops to that temp.

Most modern conventional heat pumps still have a COP around 2 at 17 degrees outdoor temp. Meaning for every 1 KW of power they use, you get 2 KWs of heat even when its 17 degrees outside.
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Old 12-10-2018, 10:05 PM   #10
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Re: HVAC/Heat Pump Question


Thanks for the replies. Kinda affirmed my gut feeling.

Fourth, yeah. I'm in the land of hydro now. Rates are good enough, just have that 70's gas shortage frame of mind. Oh, and I'm cheap.

Got a wood stove that came with the place. Need to get that fired up, but there's that last long piece of molding that has to go behind the flue... it's only been a little over a year now.
I really just want to get the stove going to piss off the green weenies that dictate air quality in nearby Eugene!

As to the nuke option, tough to land high grade uranium and I really don't think my weldings skills are up to par.

It's always fun here. Back to my lurking!
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Old 12-17-2018, 09:04 PM   #11
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Re: HVAC/Heat Pump Question


Personally, I would set it down while not there. I prefer the warm air coming through the vents while "occupied", and also believe, long run times is less wear and tear on the equipment as opposed to shorter cycles.


It won't necessarily save on the utility bill, but...

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