Mini-Split Heat Pump

[Mex-Busnut]

I am enjoying this thread. I would love to see some more pictures of these installed on buses, in addition to Ron's (alias twocnusa).

Thanks in advance!

[buswarrior]

as to where the HVAC goes in a coach...

The coach may be easily calculated for stationary HVAC loads, as existing residential calculators may be adapted to our use.

However, these calculations are pretty much useless for a coach that is underway.

Air intrusion is the biggest loss beyond any other, and a coach is leaky. Every seal, every opening, every crack, are all put under either pressure or vacuum while moving, sucking or blowing the conditioned interior air out and replacing it with unconditioned air from outside.

Somewhere in the past when we had the engineering experience on these boards, IIRC, it was suggested that an opening of 8 square inches was all it would take to completely overcome the big 80 000 BTU stock coach HVAC.

Add up all the little openings and it isn't hard to reach a total that will overcome a pair of roof tops.

So, a religious crusade must begin: seals have to be fresh and adjusted, all cracks and holes chased with the spray foam.

Then, there are the lesser issues of greater sunload through glass/ceiling/walls and the high heat transfer materials that the coach is typically constructed from.

And, for a driver sitting facing the sun, ambient temp in the coach isn't enough, the driver needs a steady stream of cool air to feel comfortable.

Due to the air intrusion variable, it would be very difficult to have a calculator that would for all coaches in the condition that ours are in.

So, go big, or plan for additions if you try for small?

happy coaching!
buswarrior

[jackhartjr]

I can tell you that BuddyDawgs front A/C works well and is very quiet too!Jack

[luvrbus]

I am not a AC guy but I heard the new freons run under extremely high pressure that would make me a little nervous with high pressure and vibrations from a bus using a house type system ?


good luck

[pvcces]

Cliff, you're right, but that is what makes the performance so good on the modern units. We got involved because the cost of fuel heating was too high and these draw most of the output heat from the outside air. For us, it means that we can heat for about 1/3 the cost of fuel.

A background item was that we do not have enough power to put everything on electricity, so we need a way to keep people off of electric heat. These units accomplish that.

R410A evaporates at around -80 F at atmospheric pressure, so it can work down pretty low.

For what it's worth.

Tom Caffrey

[pvcces]

Kenny, stick to the one ton units, and they should only about 24 inches tall and run on 120 V. However, a lot of the inverter units require 240 V.

Good luck.

Tom Caffrey

[Mex-Busnut]

stick to the one ton units

Mr. Tom: Please excuse my ignorance: What is "one ton" in BTU's?

Thanks in advance!

[robertglines1]

12,000btu    -Mci 8 tin tent  uses 2 ea 12,000btu and they work great in high 90's with stock insulation..40 ft coach..

[Mex-Busnut]

Thanks, Mr. Robert! How about a couple of PIX?

[pvcces]

Robert is right; one ton is 12,000 BTU per hour. The one ton term comes from freezing units that produced one ton of ice in 24 hours. That's 288,000 BTU per day.

To compare it to something simple, an electric heater of 1500 watts produces 5120 BTU per hour if it runs on high without cycling on and off.

One KWH is 3413 BTU.

One horsepower hour is a little over 2500 BTU.

A 35,000 BTU RV furnace uses .38 gallons per hour of propane. They are rated as 75% efficient, so the output will be about 26,000 BTU. You can get a comparable amount of heat out of about 5 electric heaters.

The mini-splits will use about 1 KW per rated ton of heating or cooling.

I hope some of the above is of some help.

Tom Caffrey

[robertglines1]

by the above calc  if you pay 17cents per kWh for elect and use LP at $2 Gal times .38 it would cost 76 cents for the same amount of heating...BIG difference  17 compared to 76...  I do know there are differant SER  (efficiency ratings) for ac units and that the larger the # the less energy a unit uses...please correct my memory but are nor most roof tops around 9 and are not the mini splits starting at 13 and going up to around 20...this is why I decided to go with Mini-split plus they are much quieter. Bob

[pvcces]

Robert, I have never seen the SEER ratings for an RV air conditioner, so I can't help you there. Since we are needing them for heaters more than cooling units, we are looking for the HSPF. The 13 SEER units come out about 7.7 to 8.0 as heaters, and we have seen claims as high as 11 or so.

In any case, I have heard reports of suspicions that the output ratings are not reliable. From what I've seen of the air conditioner business, not much would surprise me. We know of rooftop units drawing right at 15 amps and of some rooftop units that draw around 11 amps. That's a whopping difference in efficiency if the output is similar.

Perhaps, someone with more knowledge about these units can shed some light on this subject.

Tom Caffrey