[bfletcher7]

Hello. I am curious; what data do you experts analyze in determining if/when to allow a t-stat engage electric strips for homes with heat pump systems in, say, Ohio? Do you utilize data provided on paper, or do you monitor and calculate actual energy consumption from each source? Thanks.

 

[user_12345a]

Common sense dictates that the supplemental heat cycles on when the heatpump can't keep up. Can do many things with fancy t-stats but won't make a big difference.

 

[beenthere]

If a thermostat has aux heat lock out, or if using an outdoor stat to lock out the aux heat. A balance point graph that uses the load calc and the heat pumps performance specs.

On homes where the owner just wants to upgrade to a stat that can lock out aux heat. A best guess based on other homes in the area. Along with the instructions to the HO on how to reset the lock out temp.

Keep in mind, that a home that has the aux heat locked out until 20°F, may do fine during the day, but lose a few degrees temp during the night, due to loss of solar heat gain.

Aux lock out benefits those people that like it a bit cooler when they sleep, then during the day. And don't want to constantly be paying for the aux heat to do the heat recovery work, that the heat pump can do, but takes much longer to do.

 

[Bob Sanders]

Your machine should come with a data sheet and provided your system was properly installed/maintained that data sheet should be fairly accurate. It will tell you to what temperature and COP the machine is good for, and as long as your COP shows a better performance than heat strips then you save money by running your pump. (BT says once the cop hits 1.3 then it's not really worth it because the defrost sessions eat up that savings.. and that sounds logical to me.)

Above that COP, anytime you run the heat strips you're wasting money. Now that doesn't mean you shouldn't run heat strips. If your pump isn't big enough to keep up on its own then obviously you need to fire up the heat strips. But the mistake people make is locking out their heat pump too early and losing that savings. This is why with heat pumps it's best you go out and buy a high end stat which allows maximum and detailed control over your heat strips so you can maximize savings.

My data suggests my pump is good to -10f with a cop of 1.67 (btu output of 15,500) so I will let the pump run until at least that temperature and the thermostat will subsidize with heat strips as needed.

Now I know for a fact (with some experimentation) that I don't need heat strips at all down to about -2 or -3 so they're just plain locked out until that point, but after that they're not necessarily on, but are available to subsidize the pump's output if and when needed.

It's not hard to experiment in your area... just disconnect the heat strips and find out to what temperature your pump will hold its own to.

 

[user_12345a]

It's all automatic unless you shut off the system or set back the t-stat. otherwise the strips will only come on when needed.

If you or someone else feels the need to change the temp, then it may make sense to put a lockout on or something.

 

[bfletcher7]

Thanks Bob & Been for the helpful detail!

 

[bfletcher7]

Regarding COP, am I allowed to post a clip of my Lennox XP13 ratings manual in hopes of receiving some additional guidance?

 

[Bob Sanders]

Regarding COP, am I allowed to post a clip of my Lennox XP13 ratings manual in hopes of receiving some additional guidance?

I believe as long as your Lennox and its ratings manual are properly dressed, are not racially biased, are not uttering swear words, and there are no Xrated portions of your clip, you are free to post away. :smile:

 

[supers05]

I believe as long as your Lennox and its ratings manual are properly dressed, are not racially biased, are not uttering swear words, and there are no Xrated portions of your clip, you are free to post away. :smile:

....oh dear....

Cheers!

 

[beenthere]

Regarding COP, am I allowed to post a clip of my Lennox XP13 ratings manual in hopes of receiving some additional guidance?

Yes you are.

 

[bfletcher7]

Okay, so here is some data from my heat pump and air handler/heat strips. The guidance I'm seeking is--well--I'm clueless about how to make the decision to supplement the HP with electric and when to lock out the HP entirely. Can you help? Here are some points:

1. The HP data shows a CBX32MV air handler; mine is CBX32M (non-variable) blower
2. I'm making an assumption that my heater box is ECB29-25CB because a) at the air handler there are connections to W1, W2, and W3, making me think I have 3 stages and b) I have three 50A breakers.

All I know is that I measure temps in the 90*'s at a nearby register with outdoor temps in the low teens (from only the HP). That raises a point about an earlier post where we spoke briefly about my supply temps and a couple of you remarked that it seemed too high. With using the Prestige stat over the past week I've learned that my return temp usually hovers at 77* with a set point temp of 72*. Is that because we're in a two-story home utilizing one unit and no zoning and all of our returns are on the second story? What issue(s) does that pose?

Thanks again for any help you can offer!

 

[Bob Sanders]

You should have a performance chart which lists cop and such at different temps that looks something like this (from my Goodman 4 ton)

 

[beenthere]

Okay, so here is some data from my heat pump and air handler/heat strips. The guidance I'm seeking is--well--I'm clueless about how to make the decision to supplement the HP with electric and when to lock out the HP entirely. Can you help? Here are some points:

1. The HP data shows a CBX32MV air handler; mine is CBX32M (non-variable) blower
2. I'm making an assumption that my heater box is ECB29-25CB because a) at the air handler there are connections to W1, W2, and W3, making me think I have 3 stages and b) I have three 50A breakers.

All I know is that I measure temps in the 90*'s at a nearby register with outdoor temps in the low teens (from only the HP). That raises a point about an earlier post where we spoke briefly about my supply temps and a couple of you remarked that it seemed too high. With using the Prestige stat over the past week I've learned that my return temp usually hovers at 77* with a set point temp of 72*. Is that because we're in a two-story home utilizing one unit and no zoning and all of our returns are on the second story? What issue(s) does that pose?

Thanks again for any help you can offer!

Lowest COP listing at 17°F is 2.36, so no reason to believe you will be below 1.6 at 0°F outside temp.

A 77°F return means you lose a bit of efficiency. The warmer the indoor air temp, the less efficient a heat pump is.

And yes, its caused by having all high returns.

 

[throrope]

Unless you have something strange, it is much simpler.

Many heat pump thermostats are permanently configured to kick in the auxiliary heat when the space temperature is three degrees below set point. The thought is if the heat pump can't keep the space within three degrees, the losses are greater than available capacity. The outside heat pump condensing unit often has an ambient sensor that prevents operation at lower than rated temperatures and effectively disconnects the logic between the thermostat and condensing unit.

This standard configuration is why most advise against using a setback thermostat for heat pumps. The auxiliary heater electric use an cost during return from setback typically exceeds the savings.

The game is changing with new thermostats. I recently installed a Emerson Sensi WIFI thermostat on our vacation home's heat pump. This thermostat has a software driven auxiliary heat lock-out that prevents operation of the electric strip heat. The system will only use the heat pump condenser for heating no mater how far from set point. This for me opens the door for setback schedules. The WIFI feature enables me to check house temperature from our primary residence 400 miles away and change set points, operating schedules and auxiliary heat lock-out. In the past the house had to be cooled with or without our presence because it would take two days to get to cool during a week's vacation. Now I kick-in the AC on the Thursday before our Saturday arrival and avoid the intervening utility costs.

Hope this helps