Trane XL16i running all the time at cold temperatures - Is this normal?

[s012adh]

Hi! Last May I got a Trane XL16i heat pump installed and so far have been very happy with it. With it getting colder outside, I have noticed that it runs constantly if the temperature is down in the mid 20's or lower and wanted to see if that is normal when having the house set at 68 degrees. I have the Trane thermostat (the 802) with the outdoor temperature sensor. With having a thermometer at one of the vents, I can see that it switches from the first stage (With outside temperatures in the low 20's, I see upper 70's coming out of the vents) to second stage (With outside temperatures in the low 20's, I see mid to upper 80's coming out of the vents) occasionally. Then after several minutes in second stage, it kicks back down to first stage. I guess I would have expected it to stay in second stage as long as is needed and then have the air completely kick off once the desired temperature is reached (like my old heat pump did). If I raise the temperature a couple of degrees to kick on the auxillary heat banks, temperatures get above 100 quickly. But then after several minutes, the air kicks back to a lower stage instead of having the air kick off completely. Is what I am seeing normal operation with this heat pump? Thanks in advance for any responses!

Aaron

[kilowattdiver]

That's the problem with most heat pump thermostats when the temperature drops below the balance point.

I use two different solutions for my customers to chose from. One is to use an outdoor sensor or stat to bring on one bank of electric heat when the temp drops below 25 or 30 degrees along with the heat pump. The other solution (and the easiest and cheapest) is to just use a Braeburn model 3200 (non programmable) or model 5200 (programmable) thermostat to run the system. With these stats and an all electric system the heat pump will always run on first call for heat but if it fails to maintain the set temp and the house continues to get cooler the second stage will call for the electric heat strips to come on and then KEEP THEM ON UNTIL BOTH CALLS FOR HEAT are satisfied, at which time the system will shut off. On the next call for heat the heat pump starts by itself and the cycle starts over.

This system is an easy one to use and still take advantage of the heat pumps ability to produce heat at colder temps while keeping the customer happy with warmer supply temperatures.

Hope this helps.

Kilowattdiver

[a/c-harris]

is the trane 802 t-stat the touch screen one? if so that t-stat can be set to lock out heat pump at a certain temp and bring on electric heat strips. this would be the best option. Have your installer set this up.

[jrbenny]

Why is it a problem if the heat pump is maintaining setpoint? Why do you want to waste electricity?

If your customers are complaining about cold discharge temperatures, you need to select registers that don't throw air on them. You also need to educate your customers on the proper operation of a heat pump system.

To the OP, there is nothing wrong with your heat pump running as you describe. The system is maintaining temperature in the home. As it gets a bit colder, you will see it staying in high stage longer. Eventually, it will start cycling AUX heat while the compressor continues to run on high stage.

I have a 5-stage HP system in my home. Once it's in the 20s the HP never stops running. When it's in the mid to high 30s, the heat pump may actually stop from time to time. It depends on the wind and how often we open the doors.

Heat pump systems are not designed for you to stand on the grill to warm yourself. As you've noticed, they have air temperatures that are less than your skin temperature.

Enjoy the low cost heating!

[Airmechanical]

I have a 5-stage HP system in my home.

5 stages?, does that mean 2 stages heat pump, with 3 stages of 5 kw each:cool:


.

[beenthere]

A 2 stage stat wouldn't help either. Thats a 2 stage outdoor unit, plus strip heaters.
Better known as a multistage stage heat pump.

Your current stat can be set for the second stage to satisfy the heat call if you really want it to.
Just adjust the CPH of the second stage to less then the first stage CPH.

But its doing what it is suppose to do.

[jrbenny]

5 stages?, does that mean 2 stages heat pump, with 3 stages of 5 kw each:cool:


.
Keyword...

system


Yes, you are correct.

[FSHnFRK]

jrbenny:
If the system NEVER shuts off than yes there is a problem. The unit should be bringing on stages of aux heat strips as needed than bring the room up above desired setpoint than cycle off. Hopefully the home is insulated well enough and the equipment sized properly to maintain and or get to desired temp! Have the tech come back and reprogram the stat so that this happens.
Good Luck:)

[jrbenny]

Nope.

If the system is below the balance point of the structure, then the heat pump should continue to run. Modern thermostats have enough control built into them to prevent overshooting first or second stage. So, the aux heat is secured before satisfying the call for heat pump.


With it getting colder outside, I have noticed that it runs constantly if the temperature is down in the mid 20's or lower and wanted to see if that is normal when having the house set at 68 degrees.

Mid 20's or lower is most likely below balance point of the structure.

[s012adh]

As far as the system shutting off...As soon as the outside temperature reaches about 30 degrees, it shuts off once the set temperature is reached. So it sounds like the system is running like it should. Being that it runs differently than my old heat pump does, I just wanted to make sure. Thanks to all who responded..

[FSHnFRK]

If the unit is running below the balance point without aux heat it is a waste. Once you reach that point of 1/btu for 1/btu and the compressor continues to run your not gaining anything. You than need aux heat to overcome this point. It sounds to me the aux heat is not coming on soon enough. These are just opinions would love to see it first hand.
:)

[jrbenny]

Not an attempt at being argumetative...

You must be well below zero °F to get a COP less than 1.

[a/c-harris]

this is a stupid thread. At my house I have a heatpump with same t-stat and an outdoor sensor. I noticed that at below 30 degrees is doesnt warm the air very well, so i set it up to bring on backup heat in those situations. Since I live in dallas we dont get below 30 degrees very often. So anything above 30 degrees the stat is set up to not allow electric heat to come on. This is common practice, I dont know why everyone in arguing.

[beenthere]

Since I live in dallas we dont get below 30 degrees very often. So anything above 30 degrees the stat is set up to not allow electric heat to come on. This is common practice, I dont know why everyone in arguing.

If you lived where it got cold in the winter, you would know why. :)

[captain air]

looks like it is running ok
1st stage is going to raise the temp only to a certain point when it cannot keep up. The stat then brings it to 2nd stage and then the strip heaters and ten back down to 1st stage to try to mantain set point temp
being the temp is in the 20:s and the system is mantaining 68 and you are comfortable you doing good

last thing you want imo is to rely on those electric strip heaters \ you bill will go through the roof

[mayguy]

I agree, there is nothing wrong with your system.. That is normal, that's the ideal behind a two stage system = long run time for comfort!

If the t-stat's 2nd stage can't keep up, then the Aux will kick in to help out and goes back to 2nd..... 1st.. as needed.

So, sit back and enjoy the new system and knowing you are saving money by running the heat pump steady vs having the electric heat cycling the t-stat on and off.

I have a two stage gas heat, and when we are 0˚F or colder, the 1st stage pretty much runs none stop, and cycles 2nd stage every now and then.

[firecontrol]

Possible decription of the perfect heating system: One that puts exactly the amount of btu's into the structure that are being lost and runs 100% of the time that the outdoor temperature is such that setpoint can't be maintained without the addition of btu's.

Why you ask.........

Well it's like this....... if the area near the floor is getting cold the occupants will be uncomfortable (cold air sinks). This happens at different rates in direct proportion to the temperature difference between what you're trying to maintain in the home and what it is outside. The rate it happens is a result of the amount of btu's that are leaving the structure. To replace these in the exact amount that they're leaving results in PERFECT comfort. And IMO the ultimate in efficiency.

[allan38]

Your two stage heat pump is doing exactly as it was designed.
The second stage is coming on when the first stage doesn't keep up.
The first stage runs almost all the time to match the heat loss from the home.
Total wear and energy consumption is very low because the continuous run time reduces the amount of startup wear and current surge .
Longer run times reduce air stratification within the home.

Still the thought of the system running constantly drives some people nuts.:D

[FSHnFRK]

In the origianal post he said it is not reaching setpoint! (unless I miss read) If I did soooooo sorry! :D

[beenthere]

He didn't say it wasn't maintaining set temp. He said it doesn't shut off.
Its maintaining his set point (68*), but is running constantly when the OD temp is below 20*. And he thought it should shut off.

[FSHnFRK]

If it is reaching desired temp shouldnt the unit cycle off, or does the compressor (1st stage) run continuosly? If this is the case than I just learned something about this system.
Thanks:D

[beenthere]

The stat is keeping it on, because the stat is not set up to completely satisfy the heat demand on second stage when its below first stage balance point ( a couple tenth of a degree).
Its a comfort feature that can be disabled. But why buy a comfort system and then defeat its ability.


Some 2 stage heat pumps have a lock out temp that they will automatically go to second stage heat pump after the OD temp gets to that lock out temp.

[mark beiser]

If it is reaching desired temp shouldnt the unit cycle off, or does the compressor (1st stage) run continuosly? If this is the case than I just learned something about this system.
Thanks:D

The thermostat utilizes the available stages of heat to maintain the set temperature as closely as it can, without overshooting.

If the outdoor temperature is blow the balance point, the heat pump, or first stage of a multistage heat pump, will run continuously.
The thermostat will cycle 2nd stage of the heat pump, and the electric supplemental heat on and off as needed to maintain the set temperature, but won't cycle the system completely off unless it starts to overshoot the set temperature.

The idea is to do as much of the heating as possible with the heat pump, since it costs less per BTU of heat than straight electric heat, even down well below 0º outside.
Cycling the heat pump off when it doesn't have to be cycled off also reduces the systems efficiency a lot.

It is also a more comfortable way to operate the system, since you don't get the constant swing of the house heating up, then cooling down.

[kilowattdiver]

Sorry I didn't log on sooner as I see I've missed a lot of conversation about this subject.

Benny makes some good points about how the system was set up to run and how his 5 stage heat pump works. Just one problem for most people, myself included. Is the system efficient? And is it comfortable? For me there is a fine line somewhere with any all electric heat pump system where I give up on saving a few pennies and opt for some comfort.

It's like be married, meaning we all have to compromise once in awhile. I personally think all HP systems should have a plenum sensor set to monitor the discharge temperature to make sure we maintain a certain temp which the customer can feel comfortable with. Someone also mentioned schooling the customer on how a HP system works, which should be SOP for every installer worth his salt. The problem is everyone (especially older homeowners) have a different idea of what is comfortable to them. Hence we could argue about this until the cows come home.

I'm just happy to see some interest in heat pumps. They are a great alternative heat source and very competitive if your electric rates are reasonable.


Blue skies,
Killowattdiver

[docholiday]

Blue Skies? Sounds like a skydiver. Ol' DocHoliday used to punch clouds but gave it up about 8 years ago.

[OOC]

I could certainly see that, Firecontrol. Nicely put. Like you said, the rate of heat loss from inside to outside is directly propertional to the temperature difference between the inside and outside. (heat loss = overall heat transfer coefficient times surface area of your walls&ceilings times the difference in temps between inside and outside (q = UA(T1-T2) ).

So if a tstat overshoots and warms your house 1-2 degrees warmer than your setting, your rate of heat loss is greater i.e. you're losing more BTUs during that time of overshot than you would lose if the setting was dead on. Thus you wasted the energy you put in the house from the setpoint to the point the system stopped at the overshot temp.
Which from my understanding is why variable speed air handlers/blowers and multi-stage HPs and furnaces came about anyway... to try to eliminate the under and overshooting of your setpoint from sharp temperature changes, to softer, more attenuated temp changes. Minimize the area under the curve between the setpoint temp and actual temp on a graph of actual Ts versus setpoint. Anything above the setpoint you're wasting heat, anything below the setpoint you're not comfortable.

[kilowattdiver]

Blue Skies? Sounds like a skydiver. Ol' DocHoliday used to punch clouds but gave it up about 8 years ago.

You're right, I am a skydiver. Have been for about 15 years and 1700 jumps.
Seem to be slowing down myself. Too many other things going on.