Heat Pump?

[gaylejoe]

Sometimes we hear two different motors running when using the heat pump. The fan will shut off and we can still hear another motor running. Is this normal? This past weekend we used it with outside temps in the upper 20's and if it froze up we were not aware of it. This our first heat pump and we are just trying to get use to it.

[jcanavera]

Originally Posted by gaylejoe

Sometimes we hear two different motors running when using the heat pump. The fan will shut off and we can still hear another motor running. Is this normal? This past weekend we used it with outside temps in the upper 20's and if it froze up we were not aware of it. This our first heat pump and we are just trying to get use to it.

The heat pump function has a fixed time limit in which it runs. Once it hits that time limit, the blower shuts down and the heat cycle reverses itself. What you hear is the compressor running. This causes the outside coil to heat up and melt any ice that may have formed on it. When you are in heat pump mode that outside coil gets cold and the inside one gets hot. When in air conditioning mode it's completely reversed.

First time you hear this, you think something has failed on the unit. Once the defrost cycle has ended, the fan will kick back on and the system will go back to heat mode.

Jack

[Wingeezer]

Slightly off topic, but we too are new to having a heat pump in our trailer.

I am wondering what, if anything, is the advantage when compared to just using one of those small ceramic cube heaters when on shore power?

We did use the heat pump for the first time on a trip south last winter, and it did work, but not great, and to my mind no better (maybe worse) than the little elec heater we have kept from our last trailer.

Seems to me to be little point in wearing out my AC compressor to run the heat pump compared to a $25 elec heater, so my preference so far is not to use it and just carry on using our little elec heater on cooler night.

Am I missing something? I wouldn't think the heat pump is more efficient, but maybe?


Brian

[moosetags]

We have used our heat pump extensively (500+ nights of camping) and have found it meets our needs in most cool to cold circumstances. The first time that we used the heat pump in below freezing weather, it made strange alternate fan noises as jcanavera describes. We thought we had broken the darn thing. Since then, we use the heat pump in most cool weather circumstances, but we go to the gas furnace when the outside temperature drops below freezing.

We feel that the heat pump works very well and use it often. I don't believe that using the heat pump will at all shorten the life of the unit. On the contrary, not using the unit at all for long periods of time may cause seals to dry out and become prone to premature failure.

Brian

[ROBERT CROSS]

We too have used it extensively in above freezing temps. Works so well the Polinis has stayed in the closet.

Brian hit the rivit squarely, non-use is one of the main causes for AC/heat pump failure.

[2dabeach]

Originally Posted by Wingeezer

Slightly off topic, but we too are new to having a heat pump in our trailer.

I am wondering what, if anything, is the advantage when compared to just using one of those small ceramic cube heaters when on shore power?

We did use the heat pump for the first time on a trip south last winter, and it did work, but not great, and to my mind no better (maybe worse) than the little elec heater we have kept from our last trailer.

Seems to me to be little point in wearing out my AC compressor to run the heat pump compared to a $25 elec heater, so my preference so far is not to use it and just carry on using our little elec heater on cooler night.

Am I missing something? I wouldn't think the heat pump is more efficient, but maybe?


Brian

Brian....The main advantage of using the heat pump over a plug in electric heater is if your paying the electric bill. A typical plug in electric heater rated at 1,500 watts (12.5 amp) will provide you with 5,118 BTu of heat into your trailer. Heat pumps use the reverse refrigeration process and are able to get more output for the same amount of electric being consumed. A typical heat pump rated at 1,370 watts (11.4 amps) will provide you with 11,600 BTu/hour of heat into your trailer. That gives you 2.5 times more heat for the same amount of electric consumed. The only problem with a heat pump is that it loses it's efficiency as the outside temperature drops below 40F. Many of the units will shut down as the temperatures drop below 35F-40F and switch over to your propane furnace.

[Wingeezer]

Thanks for the feedback on advantages of using the heat pump! Appreciated!


Brian

[Boondocker]

I have a heat strip on the new Carrier low profile, I don't think it works the same way as described here. It is a sperate piece that bolts into the ducting of the AC. It has a copper tube that gets hot. I didn't know you could get a true heat pump option. Live and learn I guess.

[Wingeezer]

Out last trailer had the heat strip setup, the AS has the true heat pump.

I was familiar with the operating principles involved in both, but didn't realize the magnitude of the efficiency comparison.

I suppose it must vary quite a bit though, depending on the outside temp?

Brian.

[azflycaster]

Originally Posted by Gen Disarray

I have a heat strip on the new Carrier low profile, I don't think it works the same way as described here. It is a sperate piece that bolts into the ducting of the AC. It has a copper tube that gets hot. I didn't know you could get a true heat pump option. Live and learn I guess.

The heat strip is a nice option. I have one on my Carrier LP. It worked very well when I was in Fort Collins this October. Unlike a heat pump, it works equally as well regardless of the outside temperature.

[vswingfield]

Originally Posted by Gen Disarray

I have a heat strip on the new Carrier low profile, I don't think it works the same way as described here. It is a sperate piece that bolts into the ducting of the AC. It has a copper tube that gets hot. I didn't know you could get a true heat pump option. Live and learn I guess.

The behavior discussed in the earlier posts is from owners of newer Airstreams. From their descriptions, my guess is that these are ducted systems with a wall thermostat, not self-contained (Freeblow in Carrier speak) rooftop units.

I installed a Carrier 15,000 heat pump model at the end of March, 2008 (http://www.airforums.com/forums/f427...ead-40795.html), so this is my second winter to use the heat pump. Mine is a self-contained unit like yours, I'm not sure when the switch to the ducted models took place in Airstreams, but it was after 1983. The fan runs full-time like the AC, so the behavior gaylejoe described never comes up. The fan noise covers the defrosting cycle that Jack discussed in his reply. The self-contained heat pump models also have a heat strip (just like yours), so they switch to the heat strip when the temperatures drop low enough for the heat pump to lose efficiency. The ducted models switch to the Airstream's furnace.

I find that the heat pump works very well here in central Arkansas. It rarely gets cold enough to switch to the heat strip, but when that happens it does so just fine. I only had the furnace on a couple of times last winter, and only for brief periods of time. So far this winter, just a test firing to insure that everything was Ok.

Given all that, I'm sure that you are going to be happy with yours. I use an electric oil radiator as my first line of defense against the cold and go to the heat pump when it can't keep up. That's what I am using right now. It's 55 outside and raining (we set a new record for the rainiest year in Arkansas history last night and it has been raining hard ever since) and the inside temp has crept up to nearly 75 with just the oil radiator. I really need to adjust the thermostat on the oil radiator a little, but I think I'll take a shower first. It is totally silent so I do use it when it will do the job.

[Boondocker]

Now I am completely lost. Are you saying the new Carrier low profile units have heat pump capacity and a heat strip that kicks in a low temps? That would be pretty cool. Or does my new unit only have a heat strip?

[vswingfield]

Originally Posted by Gen Disarray

Now I am completely lost. Are you saying the new Carrier low profile units have heat pump capacity and a heat strip that kicks in a low temps? That would be pretty cool. Or does my new unit only have a heat strip?

Hi Rodney,

Unfortunately (?..at least for definitive answers), both kinds are available. Unless you specifically bought a heat pump model, you probably have the heat strip only. Given that, you would have paid less too, so there would be some offset of heating savings in the purchase price I guess. The options are the same whether you get a low profile or, like me, the standard one. You are right, the heat pump units have the heat strip that kicks in at low temps and it is pretty cool, or would that be hot!? It does work nicely.

I went with the standard for a couple of reasons, including a few more CFM from the fan. I also decided that a 34' trailer could handle the visual impact of the standard unit, but i'll have to admit, the low profile models are good looking. More detailed information is available at Carrier Product Line. Unfortunately, you have to open and plow through a punch of pdf files rather than use a "compare" feature like some websites.

[Pahaska]

In central Texas, I use a ceramic heater when we are in the forward part of the trailer since we usually have the TV on and tht heater is quieter than the heat pump. When we go to bed, I switch to the heat pump since the heat reaches to the bedroom a lot better.

Also, with the heat pump on, the system will switch to furnace if the outside temperature goes too low. We have had that happen only a few times since our lows are usually above that point.

In the Dometic systems, the fan goes off during the defrost cycle. Apparently that doesn't happen with the Carrier according to previous posts. That would tell me that the Carrier is going to blow a lot of cold air during defrost.

[jcanavera]

Problem with the heat strips is that there is no thermostat control. You get cold, you turn it on. It gets too warm, you turn it off.

There is one other issue with the heat pump. If that defrost cycle isn't long enough, the unit freezes up. I had that happen in Branson one October. It rained all day, temps were in the upper 30's. With the outside humidity extremely high the cold outside coils condensed ice on them. The unit did it's defrost cycle but due to the humidity, the ice didn't completely thaw. Well this was going on all day and by the time we got back to the trailer that evening I found the trailer inside was cold with the heat pump blowing luke warm air. I pointed the flash light on the outside of the trailer and found the outside coils encrusted in a block of ice. The next morning I went out and took this picture. You can see the coils still hadn't defrosted. I still use the heat pump, I just exercise a little restraint when the temps reach 40 and it's extremely humid outside.

[blickcd]

I also installed a Carrier AirV heat pump about year and a half ago. Part of the reason I got it was the fact that it would automatically switch on the heat strip instead of constantly defrosting when the temperature outside got too cold. This is the standard profile unit and it looks okay on a 31' trailer.

Something I heard but don't know for a fact is that Carrier stopped making these. Maybe they didn't sell enough to be profitable. A real shame if that is true.

Christopher

[azflycaster]

Jack - The Carrier Unit Heat Strip does have a setting for temperature. It's a hot<->cold knob that you need to mess with to find your comfort zone. The fan does not stop when the strip powers off.

[jcanavera]

Originally Posted by azflycaster

Jack - The Carrier Unit Heat Strip does have a setting for temperature. It's a hot<->cold knob that you need to mess with to find your comfort zone. The fan does not stop when the strip powers off.

Glad that Carrier addressed that. With Dometic there was no option like that.