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Author Topic: mini-split use in bus  (Read 3579 times)
pvcces
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« on: June 27, 2008, 11:33:03 PM »

Nick, we have bought some of the Chinese mini-splits, and I've been looking at using one in the coach.

One thing that has been troubling me is that the mini-splits we've got show that they are supposed to work as heat pumps down to around 15 F. Try as I might, I have not turned up anything which tells me what to expect if the ambient temperature drops below the rating.

I can see arguments for them not working at all below the rating and for them losing effectiveness below the rating. Can you tell me if these heat pump designs are likely to have a sharp cutoff or if they are just less efficient when it gets too cold outside?

We have a couple of them installed in a building here in Ketchikan, and one of them was working in a snowstorm we had in March. It worked fine all through the storm, just cutting off for around ten minutes to defrost several times in the day.

Can you recommend any website or other reading so that I can get up to speed on this stuff?

Thanks.

Tom Caffrey
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Tom Caffrey PD4106-2576
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Nick Badame Refrig/ACC
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« Reply #1 on: June 28, 2008, 04:24:29 AM »

Hi Tom,

Your performance will ultimately lie on the brand/efficiency, and region you live in to satisfy your needs.

There is alot of junk out there, and just as many false eer ratings too. The heating side of ductless splits are far less efficient

then the cooling side.  For example, one of our local township controllers just hired us to replace 16 ductless split systems that were installed

15 years ago. The Controller did all the research allready when he came to us and knew which brand and models he wanted. He wanted

Sanyo's 20 seer inverter drive systems and I told him he is lucky because Sanyo is the only brand that I install. What he didn't know, is

that 20 seer is only on the Cooling side and the Heating side drops off steeply down to 8 seer...... The heating efficiency of a heat pump

is determined by the region that you live in. The closer to the equator, the more efficient it is.

The most efficient HP systems are Geothermal because they rely on a constant 55 deg. water temp. to squeeze heat from.


Now to answer your question, to efficiently heat your home/bus with a heat pump below 35 deg's, it needs resistance heat back-up. "electric heat"

to overcome the defrost mode or you will be left in the cold and a ductless split with a "headache"..

There are lots of sites to help you, just stay away from the brand/mfg. testimonies and stick with the HVAC installer/homeowner sites for accurate feedback.

Hope this helps
Nick-

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« Reply #2 on: June 28, 2008, 06:53:02 AM »

Tom,
    The government requires testing the 'HSPF' at 17 degrees f.  HSPF is the ratio of BTU output to watts input and at 3.413 it is equal to resistance heating.  HSPF must be the average with defrost cycles accounted for.  With that background, my minisplit has an HSPF of 7.7, so at 17 degrees the 18,000 BTU unit is only putting out about 11,000 BTU.  As the temperature falls more, the heat output will continue to fall and the energy use will stay about the same.  At some temperature the heat pump will only be as good as a resistance heater, this temperature will be below 0 and may be as low as -20. This past winter it got down to 5 degrees here, the heat pump AND 2 1500 watt portable resistance heaters kept my bus above 45 ( the temperature my Webasto would kick in at).
Regards
Jerry 4107 1120 
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pvcces
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« Reply #3 on: June 28, 2008, 08:08:42 PM »

Thanks, guys.

Both of you gave me some information that I was looking for.

Nick, what we are trying to do where we live is to get off of fuel heating as quickly as possible. Since temperatures get down to 15 F less than 10% of the time, I figured that if these work down to their rated temperature, they would do away with 80% of our fuel use. I intend to keep a sharp eye on ours this winter to see if it falls short of ratings.

We will not rely on strip heating with any of these. If we can get some of the new ones rated to zero and below, I expect that we will.

The testing conditions were something I wasn't aware of, Jerry. That information helps a lot.

It seems to me that the heat output of the heat pump when the tempterature dropped to 5 F was way down, if the 2 portable heaters were just enough to keep the Webasto off. I'll try to allow for that possibility.

In any case, I intend to maintain a pretty good backup heat source for cold spells. We live in a small town, an it's always possible to lose power in a storm or freeze, so I expect that we will have to keep some fuel available. I just don't intend to use it any more than I have to.

This spring, Juneau had a couple of avalanches that took out 100% of their hydo power. They went to diesel power and the cost jumped to four or five times the hydro cost. When it happened, they thought that the power was going to be out for around three months, but they managed to get the hydro back in around six weeks.

We just put a new furnace in our coach, and we'll probably just have one and the heat pump, rather than the two we have always had.

Traveling less, but still motorhoming in our 4106.

Tom  Caffrey
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« Reply #4 on: June 29, 2008, 07:43:27 AM »

This past winter it got down to 5 degrees here, the heat pump AND 2 1500 watt portable resistance heaters kept my bus above 45 ( the temperature my Webasto would kick in at).

Wow.  Now I feel even better about the overdose of insulation I put in our bus.  We had a week long cold surge this winter during which temps rarely got above 35 and the lows were in the low teens, bottoming out a couple times at 13 degrees.  We just have two cheap little 1500W resistance heaters from wally world.  Most of the time in the daytime we had them set at 750 watts each, and even then cycling on and off.  When it got colder at night we moved them up to 1500 watts.  This kept us up in the 70's inside at all times.
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« Reply #5 on: June 29, 2008, 11:40:05 AM »

Hitech, we're going for both; improved heating systems and insulation. The cost of fuel got us off the dime!

What we are not doing is removing old sytems that can be maintained without too much cost. I believe that we can't be sure what will happen with our energy needs, so I plan to be as cautious as possible.

The easiest way to get good insulation in an RV is to buy a S&S, but we have rejected that because of lack of safety and durability, and because most of them are way overpriced for what is included.

There is always something that needs improvement.

Tom Caffrey
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« Reply #6 on: June 29, 2008, 02:02:19 PM »

Hitech, we're going for both; improved heating systems and insulation. ...

What we are not doing is removing old sytems that can be maintained without too much cost. ...


You've probably thought this all through and come to the similar ideas or even better ones, but for the benefit of some of the new members reading this thread now and in the future I'll point out a few things that can be done to improve it without major rebuilding. 

  • Probably the best thing you can do is make sure air leaks are sealed up.  Replace or repair rubber seals that have gaps.
  • If the walls and ceiling have voids in them, fill in the voids using spray foam insulation. 
  • If you don't have insulation in the floor, I would recommend insulating the floor.  Without redoing it, you can apply rigid foam insulation to the bottom side of it.
  • Double pane windows are great, but if you don't have them, or even if you do, thermal curtains can help alot.
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« Reply #7 on: June 30, 2008, 05:21:51 PM »

Tom,

I put that film over my windows in the 30 ft Winnie.  Turned that old 74 girl into a Thermos bottle....literally.  One 1,500 w cube increased the inside temp by 30 degrees.  It had to get to 40 degrees outside before I needed the second cube and then i could maintain 70 degrees at 10 degrees ambient.  Only got to test her down to 18 degrees but the math held.  My propane, 48,000 BTU, was my backup.  The old Winnies were built pretty well but still. 

Regards to you and D.  Carolee sends greetings,

John
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« Reply #8 on: June 30, 2008, 07:17:18 PM »

Tom,

I put that film over my windows in the 30 ft Winnie.  Turned that old 74 girl into a Thermos bottle....literally.
  One 1,500 w cube increased the inside temp by 30 degrees.  It had to get to 40 degrees outside before I needed the second cube and then i could maintain 70 degrees at 10 degrees ambient.  Only got to test her down to 18 degrees but the math held.  My propane, 48,000 BTU, was my backup.  The old Winnies were built pretty well but still. 

Regards to you and D.  Carolee sends greetings,

John

I'm so confused! What film? I have read, read, read, and re-read this topic over and over and stil can't figure out what film is being referred too!  Huh BK  Huh
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« Reply #9 on: July 01, 2008, 12:54:05 PM »

Yeah, John. I want to hear more about this film, too!

If nothing else, you confirmed my point about insulation in S&S motorhomes. Now, if there is some magic film that will save us the money for insulated windows, I want to know about it.

We managed to get out fishing, yesterday, and bagged one chicken halibut, along with our first case of sunburn this year.

Doreen says Hi.

Tom Caffrey
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« Reply #10 on: July 01, 2008, 08:18:03 PM »

I am interested to know too.  I suspect it is one of the following:

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100135637

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100588592

Given how effective it was for him, I would sooner think it is the first one.  Once reasonable insulation has been attended too, air leaks are the big heat loss culprit in the winter.
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« Reply #11 on: July 02, 2008, 02:45:51 PM »

Guys,

Been using this stuff since 90 and it wasn't new then. Shocked  It is every bit as good as i said. 

The stuff RTR linked to isn't the right stuff.  His guess won't seal the window opening from drafts but might add some r value and reflect some summer sun that mine won't.  The stuff I used covers and seals the entire window opening like an exterior storm window would....but better.

I will make a trip to Home D and get you the correct part numbers and mrf model etc. Smiley FEAR NOT! Cool Roll Eyes Grin

Back in a few hours or more.

John

PS:   OOOOOHH!  Halibit....my fav.
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« Reply #12 on: July 02, 2008, 10:30:32 PM »

Tom and HTR,

The stuff is on the shelf.  62 X 210 inch sheet is $9.99 and includes the sticky tape(P/N V75).  They have a larger sheet that is for sliding glass doors. ( P/N V95)  The film DOES NOT glue to the glass and doesn't contact the glass at all.

It is called "window insulation kit" and it includes a sheet of "shrink film" and a small roll of double sided sticky tape.  The tape is high grade stuff.  I was able to pear the tape off my window frame after I had had the film up for 2 years.  The generic tape had hardened and was a real pain to get off so i eventually gave up and just taped over it for the next year.  Frost King P?N is V75 or V95 for the big sheet for doors.

The film is crystal clear and without distortion....after you shrink it.  Initially when you stick the film to the tape the film has a lot of wrinkles in it and it distorts the light.  After shrinking with a simple hair dryer it is so clear you almost can't tell it is there.  Very thin and hard....not soft plastic in the least.

I put this stuff over the windows in the door and a couple other places that don't open.  I left it on for 4 years and it never yellowed or anything.  It got a little cloudy from being washed so many times but there was no reason to remove it other than it was dirty around the edges and under the tape.

Way back when there was a product called "mylar plastic film".  It was hard and very durable and this stuff might be that all growed up and with the shrink feature.

One hint if you buy it and install it....just get it stuck to the tape and don't try for the Olympic gold for getting it completely smooth to start with.  You can shrink out some really bad sections of installation that look like a Rookie did it with just a little heating and reheating.  Don't ask how I know this.

If you stick it to metal frame the tape will sweat.  With metal framing I put Frost King P/N V25 around the metal perimeter and then stink the tape to the wood around the window. The tape keeps the film from touching the metal and there is no condensate problem.


Tom,

I will buy this stuff and mail it to you or we can maybe locate the wholesale source for a "roll" of the film.  I don't want to drive to Seattle, but maybe we can work it out so hold that as an option if you can't get it cost effectively done any other way.  Fuel is my problem as you might imagine.

What did you mean about "confirm my point about insulation in S&S".  My Winnie has 1.5 inches of foam laminate in the ceiling and walls.  The ceiling has a couple layers of 1/4 inch ply sandwiching that and the walls have a hefty plywood crash barrier that is 2 inches thick up a foot on the walls and then more foam.  The floor has 2 inches of foam down the center and is about 5 foot wide.  Her weak point is the single pane slider windows and all the metal around all the windows.  That 48KBTU furnace will drive you out of there in less than 15 minutes from a cold start and that is with or without film on the windows.  With film on the windows and 1 A roof AC going you could hang beef in there after a half hour if she is filmed.  She has given me 9 MPG "once" but her norm is 7 to 8.  The 440-3 is the best engine my sheltered life has seen.  Only use the first two barrels of the thermoquad and it will LAUNCH that 15.000 pounds of S&S from a stoplight like she was a shorty van.  The old girl, 35 years young and counting, has served me well.  Especially considering she was supposed to make one trip around the CONUS and then get pushed over a hill according to the original plan when I retired.  I loved full timing that much.   I couldn't part with her but I have always       'N E E D E D  A  B U S ".
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« Reply #13 on: July 03, 2008, 07:42:04 AM »

Thanks John!

That is a larger format version of the one in my first link.  That is what I was thinking you were talking about.  Basically it seals up air leaks and creates a dead air space similar to storm windows.
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« Reply #14 on: July 03, 2008, 07:59:23 PM »

Hi, John.

I think you must have taken my comment wrong. What I said was that one of the easiest ways to get a well insulated RV was to buy an S&S. It's much harder to accomplish the same thing in a bus!

Thanks for the information about the film. I think I understand it, now.

Back in the winter of 71-72, I drove a VW bug up the Alaska Highway, and when I went south in January, the bottom fell out. Four hours out of Anchorage, I hit fifty below. It was 60 below in Beaver Creek. After much struggle, I made it down to White Horse, and the temperature was a balmy 54 below.

I couldn't shut the engine off before I could get the car into warm storage, so I let it idle some six hours. When I came out of the lodge to move it, only one of the two small tailpipes had anything coming out. The open pipe only had a pencil sized hole left for the exhaust.

It has to be COLD out before the inside of the exhaust system will freeze up!

While I was there, someone told me to get an Arctic window for the windshield because I had to constantly scrape the ice away to see anything while I was going down the road. The window was like the film you mentioned. It was clear plastic with double sided foam on the edges.

It kept my window clear all the way to the southern border of Canada. Temps in Williams Lake got down to 50 below while I was going through. The frost inside of the car didn't thaw until after I got back into the US.

For what it's worth.

Tom Caffrey
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