Furnace usage strategy

[historyman]

When I go to work in the morning in the cold months, I've been turning my thermostat way down out of my desire to not heat my apartment when no one is in it. Upon my return in the early evening, I turn it back to 66. Indoor temps usually are in the middle or lower 50s by this point in the day and it takes the heat pump a good hour to raise the temp up.
So, here's my question: Is what I'm doing an inefficient practice as the heat pump has to work appreciably harder in order to heat the space from a much cooler intial temperature that normal?
I've heard people say that during the cold winter months, they'll leave their furnace/heat pump on during the day set to whatever temperature it normally is as they believe the furnace/heat pump has to expend less energy maintaining the temperature than climbing from a cooler initial temp.
Any opinions would be appreciated.

 

[DADoES]

50°F is not an excessively low ambient for recovery.

The trick with a heat pump is to NOT raise the temperature more than ~2°F at a time. Allow the system to cycle off, or catch up to the point of nearly cycling off, before raising it another couple degrees. If you raise the thermostat more than 2°F above the actual room temp, that will trigger the auxiliary electric heating elements, which pull a whole lot more electricity and severely reduces any potential savings. Even better, invest in an electronic/programmable setback thermostat specifically designed for heat pumps. These thermostats will keep track of how fast the indoor temp drops during the setback period and adjust how soon to start the recovery, automatically raising the temp slowly so as to not trigger the auxiliary. Look for a feature called Smart Recovery or Intelligent Recovery or something similar.

You might even consider a lower setback temp. Lower temp gives more savings ... IF you manage the recovery to keep the auxiliary out of the picture. When I did daily setbacks (I don't any longer since I'm home all day), I dropped back a full 10°F, to 60°F from 70°F.

 

[cadman]

Shouldn't there be some way to bypass the electric supplement if not desired? Then use a programmable thermostat to account for the longer rampup to desired temp. Bringing the system up 2 degrees at a time, even from 50F, sounds like a lot of babysitting.

 

[toggleswitch]

10*F is generally the largest temp. set-back believed to be acceptable for any heating system. More than that and your walls can crack and your heatng system really labors.

Hydronic (hot-water) heating systems take a VERY long time to recover such from such a wide range of a set-back.

GadgetGary's heatpump has such a smart-recovery thermosat and was being set back from 67*F to 64*F. Problem is, is that it starts heating so early in the morning to recover by the 8:30 am desired set-up time, that sleeping becomes too unfomfortably warm . His system can maintain and raise indoor temps (by heat-pump alone, i.e. not with electric coil resistance heat back-up) until the single-digits Farenheit (10*F and up). [Is that -7*C?] The smart-recovery thermostat does well to limit electric backup heat EXCEPT when the outdoor temps. at night changes for 3 or 4 days. When it has been 40*F (15*C) out at night (WARM) the system expects to recover faster,a dn it does. Follow that by a period of 10*F nights and the themrostat gets frustrated that it takes so long to recover and may call for resistance heat assitance after say 2 hours instead of the requisite 4 needed to do the job under the new conditions.

Ideally a thermal cut-out that turns off the resistance heaters above a certain outdoor temp is the best bet for economy's sake. Lacking that, a manual cut-out works well with minimal baby-sitting!

 

[gadgetgary]

Shouldn't there be some way to bypass the electric suppl

Yes

Toggles put this switch in for my system. I only have to turn on the resistance electric heat when the temps are below 10 degrees.

 

[toggleswitch]

The bottom switch is for "Electric" heat meaning eectric resistance back-up coils.

 

[toggleswitch]

The "Fan" switch is in parallel to the thermostat itself, replicating one of the thermostat's functions/options.

The "Electric Heat" switch is in SERIES with the themrostat,
meaning it can be selected to "AUTOMATIC" (control via thermostat's regular operation) or "OFF" but not "ON"

 

[toggleswitch]

YAY to "Class 2" (Low-voltage) wiring!

Both switches in the "AUTO" position menas that the thremostat is functioning without any outside "interference".... er...input from the new switches.

 

[DADoES]

<blockquote></i>Ideally a thermal cut-out that turns off the resistance heaters above a certain outdoor temp is the best bet for economy's sake.</i></blockquote>Yes, I highly recommend this, I had it done on both my heat pump systems. Even with Smart Recovery, both fell short of the target temp by just a couple degrees at the designated recovery time-of-day and triggered the auxiliary to quickly make up the difference ... which I did NOT want that happening. Much preferable to have the compressor run a little longer than to fire up those resistance elements.

 

[volvoguy87]

Saving energy.

The key to saving energy by turning down the thermostat is knowing your schedule and your system. The basic rule is the longer you are away, the lower the temperature can be set, otherwise you might end up using more energy to bring the temperature up than you save letting it decline.
Know your home and its HVAC system. Some buildings are better insulated/get better direct solar gain than others, and some buildings have better heating systems than others, so know your limits. Also, CLEAN YOUR DUCTS! I was amazed (when we replaced some ducts here) at how much dust collects inside ducts, furnaces, and AC coils, even with good filters. Clean your system and it might supprise you how much more efficient it can be.

In the neighborhood where I grew up (tract housing, circa 1986) the builder used all BOL appliances, including furnaces and air conditioners. In addition to being extremely low efficiency, it was not sized properly for the houses (all houses, regardless of size, had the same HVAC system). The ductwork was placed poorly and there were no dampers. The result was that in the summertime, the top floor would go above 90 degrees and there was nothing that could be done, and I kept a ceramic heater in my room in the winter otherwise my plants would freeze and crack the pots.
In 1996, my folks had the ductwork in the basement reworked. We installed dampers, and split the ducts so we could actually control how much air went to each floor. We also used larger ductwork for the main supplies, reducing noise. The end result was that running an inefficient, undersized furnace, we dramatically improved comfort and efficiency. It wasn't perfect, but it did help a lot. In 2001, we finally got new furnaces and AC units. We switched from 1 zone to 2 and WOW what an improvement!

In order to calculate how to save energy with a programmable thermostat, first figure out how much energy YOUR HVAC system uses maintaining temperature every hour (depending on exterior temperature). Second, figure out how much energy it uses for each hour of operation when returning the temperature to a comfortable level from a period of energy saving inactivity. Use these figures (oh no, math!) and determine what is the ideal temperature change from which your system can recover over what period of time, in order to save you money.

To borrow from another post, "Clear as mud, right?"

I like your thermostat modification Toggleswitch. Patent that and make millions by including it as a feature on new thermostats!

Sorry to be long-winded,
Dave

 

[toggleswitch]

What is that smell?

Sometimes allowing the wind to flow makes you feel better.

 

[toggleswitch]

Move over Mr. Stryker

~Patent that and make millions.

Ya know, more than one psychic has said my main source of money won't be my job.
But then again, I refuse to have any body parts casted as laytex duplicates to be sold to the general public!

Glenn, do you have pics or links of/to your lock-out device(s)? TYVM.

 

[sudsmaster]

body parts casted as laytex duplicates

Just a different sort of "job", eh?

 

[toggleswitch]

...but a girl just has to have her limits, I suppose.

Ain't nothing wrong will gathering income from royalties, commissions, rents and interest.

 

[DADoES]

Toggles, the lock-out device is an option that is part-and-parcel to the thermostat. An outdoor temp sensor (thermistor) connected to a PC board in the condensor, which activates a selection on the thermostat setup menu. Carrier Part # TSTATXXSEN01-B Temp Sensor. Cost: $40 plus an outrageous charge for installation. It looks like this --

 

[toggleswitch]

What noive - Bugs Bunny

Thanks.

An entire $40 huh?

 

[tolivac]

I had found the best bet for heat pump use that has electric aux heat-set the thermostat to a comfortable setting--and LEAVE IT THERE!don't use setback at all.At the beginning of the heat season when I started the system-both the aux heat and heat pump run to bring up the temp(the Trane system in a townhome I used to have)then the heat pump alone maintains it.If you shift the thermostat-the aux heat then comes on until the temp "catches up"to the new thermostat setting you made.Setback is fine for heat systems that don't use heat pumps or aux heat-say a gas furnace alone.

 

[sudsmaster]

Your walls can crack

And to prevent that, do you recommend the world's largest tube of Chapstick?

Seriously, around here, most older homes have cracked plaster and drywall inside and cracked stucco outside. From settlement and the constant small quakes and occasional big quakes.

I understand that the cracks that run mostly vertically are not as big a concern as those that run horizontally. At least as far as walls are concerned.