HEAT AND COOL FROM THE TONGUE BOX

[bobhenry]

The little 4x7 is proving to be a space challenge. I have been tossing about heating and cooling options. I have been doodling on paper with a tongue box exclusive for the 99 dollar 5000 btu window shaker and a thermostatic controlled catalic heater. I have drawn an oversized box that the front will open to allow the a/c unit to exhale. the unit will set on grating and drain to a sloped catch pan to drain away the condensate to the outside.

The round nose of the trailer has become a plenum after installing a straight bulkhead inside so the tongue box can vent thru the outer skin and into this plenum.

Here is where the questions start ....

With the ac unit on fan only and the heater in heat mode in the same box the hot air produced by the heater would be drawn into the inside makeup air inlet at the bottom of the front of the a/c unit and exhaust thru the delivery tube running from the cold air discharge upper vent. This cold air upper vent is sealed and all that is actually vented back into the interior. I have toyed with 2 small vents thru the bulkhead low as return air to the room air return which is sealed seperate fron the discharge side. A small power vent (fan) could be added in the bulkhead wall to aid circulation into the interior. I have the box designed so the front of it will open so the discharge side can exhale when in the cooling mode. Here is the big question can I leave the box closed in the heat mode during cold weather with just the a/c unit's fan running. I realize the outer vents are designed to cool the compressor in refrigerating mode but is it necessary with just the fan running ? The second is should I add a couple side vents on the interior return air section to draw in a small amount of OUTSIDE fresh air as well ?

[aggie79]

Bob,

I think it would work as drawn. Another option may be to move the heater to the plenum and add a door at the bottom of the plenum that you can open to function as a return air supply when in heat mode.

Take care,
Tom

[bobhenry]

Brilliant !!

Sometimes ya just gotta pull your head out of whereever it had been misplaced.




By adding a tray like drawer with a large face in the center you can mount the heater solidly by screwing thru it's base into the tray. Now just slide it in to operate and slide it out to gain access to the controls on the heater. While the flow is a a bit backwards delivering heated air up high maybe with the addition of a movable lovered discharge door over the fan I could direct the heat downward a bit. It would be easy to leave the drawer extended outward a bit to loop the heated air back to the heater to be further warmed or simply add a very small cold air return on each side thru the bulkhead wall .

Like I said brilliant !


Thank you ,thank you, thank you,

I am trying to get the other portions of the electrical ,plumbing ,and HVAC lined out before buttoning up the top and it is tough to think that far ahead.

[bobhenry]

A look at what is becoming a busy bulkhead wall




What have I missed now ?

[dh]

Bob, I don't think discharging hot air from a 'higher up'' vent will be that big of a deal, especially in a cabin that small. I have a very well insulated house, and as is common in my neck of the woods, slab construction, no basement, all ductuing in the attic, and I stay nice and toasty in December.

[bobhenry]

If not ....... a ceiling fan !

[PanelDeland]

I doubt the higher position of the heat will matter at all.As stated above the heat in a home ducted up high gradually cools and drops.It's a minor amount of temp drop though.Also just body movement in the cabin this small should help circulate air.

[bobhenry]

We have winter camped in January as a bad joke for the last 4 years and you would be amazed by the heat stratification. I took 2 thermometers a couple years running just to test this theory. In the barn the ceiling high point is 5'4" and a wall mounted thermomter was registering 105 degrees and 4 foot lower at the bed it was 64 degrees. In the clear topped (read no insulation at all) teardrop we have had it 95 plus and the bed was 56.
We liteally have rigged a small fan and used it just like a ceiling fan blowing upward and washing down the sidewalls to return the heat from the ceiling to the floor. So I really wasn't joking about a ceiling fan it really helps in cold weather.

[aggie79]

Bob,

What about having a reversible auxilliary fan? In A/C mode, it would blow into the cabin and the cool air could settle down. In heater mode, it would blow into the plenum bringing the warm air at the top of the tear down and around the heater. The heated air flow would exit at the level you want.

Take care,
Tom

[bobhenry]

Findind a small fan that is reversible has been the problem.
While the larger box and window fans have this feature I
have yet to find a reversible "small" fan. Due to size
constraints it needs to be 10" to 12" max in diameter.
For heat mode the delivery and return tubes to the a/c
cabinet would need to be blocked to stop the escape of
the heated air. Then the pressure in the plenum would
force the heated air out of the 2 small return air vents.
This now has the heated air washing the side walls low
over us while sleeping and gathering the heated air at
the ceiling and returning to be further heated and forced
thru the return ( now delivery) vents again and again.

This is getting interesting

In summer mode fan expelling cold air high into the
cabin so it can fall to be gathered thru the return vents
and recooled.

In winter (heat) mode air is drawn in high up and
reheated and delivered low along the walls.

I think this is starting to sound very do-able.

[bobhenry]

OK OK I should look further than Wally world .........

http://www.google.com/products/catalog?hl=en&qscrl=1&nord=1&rlz=1T4GGLD_enUS311US311&bav=on.2,or.r_gc.r_pw.&ion=1&biw=1024&bih=584&wrapid=tlif131306571275010&q=reversible+fan&um=1&ie=UTF-8&tbm=shop&cid=13521591886555366064&sa=X&ei=_cpDTqKBDOqOsALWl-moCQ&ved=0CDoQ8wIwAQ#