RE: How do AC Heat Strips Work?

RamblingWreck · Sep 28, 2003, 07:05 PM

Sandykayak asked this question in the " Cold Night in Florida" forum. No one has put forth an explanation, so I thought I would cut and paste the original inquiry and post under a different subject heading.

QUOTE

Would someone please explain how the a/c heat strip works. It certainly took the chill off the camper, but I left it on all night (was I supposed to do this?) and after a few hours it was starting to feel like cool a/c.

However, when I turned it off the first time I used it last year it got very cold and would not warm up when I turned it on in the middle of the night.

On the second night at Koreshan I turned off the heat strip when I went to bed but I lowered the privacy " curtain" and used an electric fan heater. This was quite OK, though I spent most of the night turning it off and turning it on again because it was aimed mostly at my face (need to find a better place to put it next time).

Comments ref the heating strip please.

UNQUOTE

Rambling Wreck

Tim5055 · Jan 26, 2003, 12:14 PM

RamblingWreckElectric heat strips are a very simple devices. They are an electric heat coil that is installed in front of the A/C blower. When used the A/C fan moves the air across the heat coil which warms the air.

They really don t have the heating capacity to warm the pop up unless it s not that cold out. You loose almost as much heat through the tenting as the heat strip can produce.

One interesting fact about these type of devices is that turning up the fans speed really makes it cooler, rather than helping warm the air. The faster moving air does not have sufficient contact time with the heating coils to warm up and the faster moving air across your body actually cools you down.

RamblingWreck · Jan 26, 2003, 02:38 PM

tim5055Hair dryers have a thermal switch. Once they get too hot, the switch turns them off. Its not possible to restart hair dryer until the thermal switch cools and resets. Do the AC heat strips have similar protection?

I was looking at a Jayco popup. The dealer indicated he could install the heat strips in the AC for about $40. He said they were suitable for mild days when you just wanted to knock the chill off the air. He pointed out that you typically pay a fixed rate for electric hook up regardless of power consumption. If you run the gas furnace on the mild days, you are going to have to refill the tanks sooner and you still paid for the electric hookup.

Rambling Wreck

Tim5055 · Jan 26, 2003, 02:58 PM

RamblingWreck

QuoteORIGINAL: RamblingWreck

Hair dryers have a thermal switch. Once they get too hot, the switch turns them off. Its not possible to restart hair dryer until the thermal switch cools and resets. Do the AC heat strips have similar protection?

I was looking at a Jayco popup. The dealer indicated he could install the heat strips in the AC for about $40. He said they were suitable for mild days when you just wanted to knock the chill off the air. He pointed out that you typically pay a fixed rate for electric hook up regardless of power consumption. If you run the gas furnace on the mild days, you are going to have to refill the tanks sooner and you still paid for the electric hookup.

Rambling Wreck

I don t know the answer to the thermal switch, but it does make sense.

I agree witht the dealer as to the use for a heat strip, but I have seen many campgrounds charge extra per day is you use electric heat or A/C

tlhdoc · Jan 26, 2003, 03:31 PM

RamblingWreckWe have a Carrier Air V air conditioner with heat. You have to get a different inside unit to have heat in the Carrier. Unlike the Coleman where you can add heat at any time. I was surprised at how much heat the Carrier produced. Our last to trips in October 2002 were with electric hookups. The temp was in the 30 s at night and the A/C produced enough heat to keep us comfortable. I only had it turned up 2/3 of the way. The other nice things about using the A/C is that you don t have to worry about anyone knocking over a portable electric heater and the A/C blows the heat into the bunkends.[

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jaycocamprs · Jan 26, 2003, 04:16 PM

RamblingWreckWe have the Duo-Therm AC unit. It has a finned electric coil right under the fan outlet. The coil is rated at just under 1500 watts. As Tim said, the air moves so fast over the coil that it doesn t warm it a lot. But it will put out lots of warm air. Not hot, but warm. Our experience has been that the heat strip and a 1500 watt portable electric heater will keep us warm enough down to freezing. The thing that I don t like about our heat strip is that it does not have a thermostat. Some I understand do, but ours doesn t. Some are also heat pumps like those used in homes. They may also have the heat strip for backup or auxiliary heat.

wssfetch · Jan 26, 2003, 07:14 PM

RamblingWreckI used the heat strip this past week when overnight temps were in teens. It kept the inside of the camper at just above freezing. One night we were in single digits and an additional ceramic heater kept the inside of the camper warm enough to be comfortable in. We have it popped up in the yard and were not sleeping in it. Probably would have had an electric blanket as well if I had been sleeping out there.

sandykayak · Jan 27, 2003, 05:57 PM

RamblingWreckthanks so much, R wreck, for posting this as a separate issue.

Mine is a Carrier a/c and the dealer charged me $100 to install it when I bought the popup (new).

You can definitely feel that it takes the edge off the interior chill.

My main question is How long is it supposed to do this as it definitely felt as if it was blowing cool air in the wee hours?

Do you leave it on all night?

In Fla state parks they charge an extra $3 or so/night for electricity.

tlhdoc · Jan 27, 2003, 07:44 PM

RamblingWreckI left ours run all night on the last 2 trips. If you get hot you can turn it off.

RamblingWreck · Jan 27, 2003, 08:38 PM

sandykayakMy pleasure to repost, I m getting an education in the process.

Looks like Tracy and the gang have the same model as you. They indicate that they were only running at 2/3 speed and ran it all night. My guess is at this speed the air is moving by slowly enough that the heat strip has a chance to warm it.

If you had your fan running at full speed, the heat strip may have been able to warm the air during the early evening hours when temperature out was only cool. As the night progressed the air outside got colder. The colder air with fan at full speed was moving by the heat strip too quickly to have a chance to fully warm.

FYI, the quote the dealer gave me for installing heat strip was a " shirt cuff estimate" . He didn t have his price book in hand. Secondly, it was contingent on my purchase of a specific 2002 popup carry over he has had in stock for a while. We both understood the final price might very a little but would be in general ballpark.

Rambling Wreck

tlhdoc · Jan 27, 2003, 08:52 PM

RamblingWreck

QuoteORIGINAL: RamblingWreck

My pleasure to repost, I m getting an education in the process.

Looks like Tracy and the gang have the same model as you. They indicate that they were only running at 2/3 speed and ran it all night. My guess is at this speed the air is moving by slowly enough that the heat strip has a chance to warm it.

If you had your fan running at full speed, the heat strip may have been able to warm the air during the early evening hours when temperature out was only cool. As the night progressed the air outside got colder. The colder air with fan at full speed was moving by the heat strip too quickly to have a chance to fully warm.

FYI, the quote the dealer gave me for installing heat strip was a " shirt cuff estimate" . He didn t have his price book in hand. Secondly, it was contingent on my purchase of a specific 2002 popup carry over he has had in stock for a while. We both understood the final price might very a little but would be in general ballpark.

Rambling Wreck

It wasn t running at 2/3 speed, the heat was set 2/3 of the way to the hottest setting. The fan runs on hi or low, but the temp. is adjusted with a dial.[

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Wayfarer · Jan 27, 2003, 09:39 PM

RamblingWreckNot trying to steal the string, but FYI we camped out the weekend of Jan 17-19, 03, at Brazos Bend SP, TX, and the temps were either side of 25 at night and high 30 s to low 40 s during the day. Our Coleman doesn t have a furnace or heat strip but we were very comfortable with two ceramic heaters from WallyWorld plus an electric blanket at night. Works well for us. Any colder at night and we might have a different opinion.

mrflinders · Jan 28, 2003, 01:50 PM

RamblingWreckI am getting ready to have an AIRV (Carrier) A/C unit installed in our PU, and I think I am leaning towards the Heat pump model. It weighs 4 lbs more than the standard model and provides 15000 btu of heating, quite a bit more than the heat strips, which provide about 5600 btu.

Does anyone have any experience with the Carrier Heat Pump?

RamblingWreck · Jan 30, 2003, 08:39 PM

mrflindersI am not familiar with the particular heat pump unit you are looking at. My experience has been with residential units. Below is based upon my observations growing up and a thermal dynamics course I took close to 30 years ago.

Heat pumps are popular for cooling and heating homes where I grew up in southern Georgia. Perhaps slightly over simplified they are heat exchangers.

They are most efficient when there is not a great deal of difference in the outside and desired inside temperature. Example 90 degrees outside and you want to cool the inside to around 70 degrees.

Our power bills would always be higher in the winter when the outside temperatures were in the 30 s and 40 s and we wanted to warm the inside to 70. Part of the increase was due to auxilary heat strips being used to augment the heat pump.

Modern heat pumps are more efficient. My father replaced his since I left home and the new unit cut his electric consumption 40%.

Heat pumps are making inroads in the northeast where we live now. Here they bury a lot of pipes below the frost line. At this depth the ground temperature is fairly constant, close to about 55 degrees. So there is not a big difference between the 55 degree ground temperature and desired 70 degree indoor temperature.

If I were shopping and knew I would only be camping in comparatively small temperature extremes, I would give serious consideration to a heat pump. Realizing of course that this decission would tether me to a 30 amp hookup or carring a portable generator should I need to heat or cool.

For large temperature variations I might lean toward an A/C with traditional compressor and a LP gas furnace.

Rambling Wreck

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