heat pump a/c

[crown]

 hi i bought two heat pump a/c a while back  do these give off heat also and if so will they warm up the bus ?

[robertglines1]

roof top?

[crown]

yes roof top

[buswarrior]

If they are roof tops, they'll take the chill off on a cool summer evening.

If you plan to camp in anything heading towards the freezing mark from summer's evening, you'll need another way to stay warm.

happy coaching!
buswarrior

[TomC]

Heat pump A/C will give off very close to the same amount of heat as it does cooling.  But-they only work down into the 40's, where a normal heating coil would have to be used.  For instance, a 13,500btu cooling A/C will put out about 12,000btu of heating on reverse cycle, but only about 5,200btu on resistance heating.  Good Luck, TomC

[Nick Badame Refrig/ACC]

Hi Crown,

BW & Tom are correct!

Just remember, if you will be in temps that near zero often, two thousand BTU's per foot will keep you warm....

Anything less, you'll need your sleeping bag!

Happy New Year
Nick-

[crown]

hi nick i have 2 heat pumps & 2 ducted roof top all low profile any way i could say make them in to a basement type
unit i known a/c guys and a guy with a metal break thanks

[Nick Badame Refrig/ACC]

Hi Crown,

If you still live in Costa Rica, do you even need heat??

i have 2 heat pumps & 2 ducted roof top all low profile any way i could say make them in to a basement type

Now why would you want to make your life so hard by doing that? Lol

It would take alot of design changes to accomplish proper air discharge out of them...

The best way to heat your coach is either, LP unit, Webasto, or Proheats.... Way more BTU's..

Good Luck
Nick-

[belfert]

Just remember, if you will be in temps that near zero often, two thousand BTU's per foot will keep you warm....

Wouldn't that mean 80,000 BTUs for a 40 foot bus?  It seems high to me.

[cody]

I have 2 carrier 15K BTU heat pumps, they work well down to about 35F, afte that they loose ground quickly. one of the biggest factors in any heating situation is cold air infiltration and insulation, the best of heaters seem to suffer when they have to fight the incoming drafts.

[dbenck]

I have 2" of spray foam on the walls, 5" on the ceiling with double insulated windows in a MC-9
I can hold 70 Deg. F in -20 with 7.5 KW of electric heat running off the generator or shore power.
7.5 KW = around 26,000 Btu's. I have a 1500 Btu toe kick heater in the step at the door also.
Coach is all electric...no problems in 4 years..so far !

David Benck

[belfert]

I must have too much glass as I have spray foam and can't maintain any heat with as few BTUs as some of you guys.  My biggest hinderance might be trying to start out with the bus at or below 32 degrees.

The side windows in my living room are double pane, but they are a total of over 50 square feet of glass.  I also have about 50 square feet of single plane windshield.  I don't have any sort of covers for any of the windows or the windshield.

[Nick Badame Refrig/ACC]

Just remember, if you will be in temps that near zero often, two thousand BTU's per foot will keep you warm....

Wouldn't that mean 80,000 BTUs for a 40 foot bus?  It seems high to me.

Hi Brian,

2000 btu's per ft is my new rule after one of my good customers couldn't keep up with his 45,000 btu Proheat.
I installed an 80,000 btu webasto in his 45' Prevo 2 months ago and since then the bus has been to Minnasota
early December and is returning as we speak from Montreal. The webasto 2020 has kept his coach at 72 deg's
on both trips. Now, we also have an engine loop and hydronic fan coils in 2 bays along with 3 hydronic heat ex-
changers inside the coach. He is a happy camper now... Well, except for his brake lines freezing up thursday..

My Proheat 45,000 btu unit in my bus is bearly keeping my bus at 68. [It's in the low 20's here in N.J.]
This is why I am changing my whole system to an 80,000 btu Webasto now.. Complete with engine loop and
bay hydro fan units. I will be headding to Indy in 3 weeks for a Ravens game if they make it that far.. and I
WILL BE WARM!!

Dave, you have a special bus! Lol
Nick-

[Nick Badame Refrig/ACC]

Ok Guy's,

I just did a load calculation on my bus for the temps I'm expierencing here in N.J. This is what I came up with..

Givin the layered fiberglass insulation and FBBF reflective layers that I have, along with my duel pane windows,

single pane windshield, and very cold step well, I have a heat loss of 44%. Pretty bad compaired to a home...

My required BTU's to maintain 72 degrees is 64,000! That is without engine or bay loops... [R value of 5.4]

Here is how to calculate your bus! I also included insulation values of foam insulation below.

Icynene® Foam-sprayed insulation has an "R" value 3.6 per inch.


Heat Loss using "R" values:
(Bus Heat Loss in BTU's per hour) =
[(Bus Total Surface Area in sq.ft.) / (Surface Area "R" value)] x (Temperature Difference)

Temperature Difference = the difference in temperature in deg F. on the two sides of the bus surface,

typically indoors and outdoors.

Surface Area "R" value = the "R" value of the surface area being evaluated (say an insulated wall).

Heat Loss using "U" values:
(Bus Heat Loss in BTU's per hour) U = 1/R, - or in other words -
(Bus Total Surface Area in sq.ft.) x (Surface Area "U" value) x (Temperature Difference)


More considerations when measuring home energy use or heat loss
But there's more work to do for a complete answer to your bus heat loss. We need to make up a simple

table which will contain the total surface area of each type of material (since each will have it's

own "R" value) and then plug in the area's "R" value and the temperature difference. Usually we assume

the same temperature difference for all of the areas of the bus though this might be a simplification

since that may not be exactly true.


How to include the effect of wind on home energy use or heat loss
We're also missing, from this simple calculation, the effects of wind on a bus's heat loss, though a

more sophisticated version of this approach might simply adjust the temperature difference to include

the wind factor. For example, you could use a wind/temperature chart to derive the effective outdoor

temperature when it's also windy. In cold conditions, adding a wind velocity will lower the effective

outdoor temperature and thus it will increase the temperature difference across the bus wall. Use any

"wind chill factor" chart for this data. Still more sophistication of measures of heat loss are possible

by adding the effects of moisture on heat loss from a surface, but while this is important for a (sweaty)

human in cold conditions it is generally ignored when considering your bus heat loss.


Using a spreadsheet to accurately calculate building heat loss or heat gain
This is a perfect application for an Excel or similar spread sheet, listing each building surface type

(wall, window, door), it's R, K, or U value, and its total area. Adding temperature difference across

these surfaces permits a calculation of the heat loss (or gain) through each surface type. These are

simply added together to represent the entire building's heat loss or gain.


Heat loss vs. heat gain in buildings: applying the simple laws of thermodynamics
You may have noticed we keep talking about heat loss and then we add "or heat gain" in the same sentences

or headings. That's because heat loss analysis works just fine for both bus heating and bus cooling. The

only differences between looking at heat loss and heat gain for a bus are the direction of heat flow and

the fact that we may be using different equipment with different equipment efficiencies (a heating furnace

or boiler versus an air conditioner).

If we're in a heating climate and are in the heating season, heat will flow from the bus interior to the

outdoors.

Nick-

[buswarrior]

Oh, ok.

It all depends on whether the BTU's can be delivered to the interior completely, or only partially.

Electric heaters, all the BTU's will be delivered to the interior, no where for any of it to go.

The coolant furnaces/boilers may inhale fuel for certain BTU ratings, but they are dependent on the installed radiator/fan systems to shed the BTU's to the interior, and have losses to the exterior in exhaust heat.

Same for a propane furnace, some heat overboard in the exhaust.

So, it still needs a bunch of thinking, we can't just throw BTU numbers around?

happy coaching!
buswarrior