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u3b3rg33k 04-12-18 01:14 AM

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I have some thoughts on this :)

I've looked at the commercially available units (there's one on the US market), at heat recovery ventilators, energy star dehumidifiers over 100qt/day, at high drying efficiency PTACs and hospital sized AHUs.
Also I have an electric dryer vented indoors (thanks to stupidity of the previous homeowners).

my thoughts are to do this:

dryer vent --> some kind of easily cleanable (and GOOD) filtration, probably down to MERV8
filtered air into an HRV to bypass thermal energy around the dehumidifier (so that the head pressure doesn't blow it up), and to lower the air temp to the evaporator for better performance-->into the dehu to dry and heat the air, back to the HRV to pick up the thermal energy, then into the dryer - air is just a working fluid.

like this (horrible drawing):

the problem with the unit on the market is cost (wow they cost a lot) and apparently dust fouling of the heat exchangers. they offer a heat pump only mode, as well as heater assisted mode (heat up with heater then switch to heat pump once the water is evaporating, instead of waiting for compressor waste heat to raise the temp of the water/clothing mix).

a major advantage (aside from not using resistive heat to dry clothes), is the lack of conditioned air being exhausted (and replaced) from your house. assuming a dryer moves 200CFM for 45 minutes, that's a lot of hot humid air infiltration in texas, or cold dry air infiltration in canada.

oil pan 4 04-12-18 02:20 AM

That's exactly what I was not going to do.
Discharging the waste heat and dust/lint outside and cooked air inside solves a lot of problems.

u3b3rg33k 04-12-18 11:06 PM


Originally Posted by oil pan 4 (Post 58988)
That's exactly what I was not going to do.
Discharging the waste heat and dust/lint outside and cooked air inside solves a lot of problems.

exactly, wow! ;)

I would argue that the waste heat isn't waste heat, but rather money being wasted. yes, the lint is a problem, and im not quite sure what cooked air is. the other issue is air infiltration. 100% of the air you exhaust must be replaced (an issue with a standard dryer as well) by unconditioned air, which then needs conditioning.

I would think the lint could be handled by a couple of extra wire screens, perhaps a minisplit style screen, and depth loading filter after.

one of the issues with portable AC units is they generally attempt to use the condenser to evaporate the water that was condensed on the evaporator side - both to increase efficiency, and to avoid the need for a condensate pump and drain hose. not sure what yours does, but if it does evaporate the water it will hinder the drying process.

if your exhaust air is adequately dry, have you considered a "hot box" with a drying rack in it, instead of a dryer? longer drying times mean the clothes tumble longer, which probably increases wear on your clothes. if you were using the AC unit for comfort, then you get dry clothes purely as a byproduct, instead of running the AC for drying? that may be semantics though.

jeff5may 04-14-18 03:39 PM

Use concentric ducts. A dryer duct inside a stove pipe works pretty well. Make sure to slope the duct so the condensate will drain.

oil pan 4 04-15-18 10:32 PM

Cooled, not cooked.

The rig is going out in the garage. No air infiltration into the house.
Didn't I put all this in original post?

u3b3rg33k 04-17-18 02:49 PM

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Originally Posted by oil pan 4 (Post 59020)
Cooled, not cooked.

The rig is going out in the garage. No air infiltration into the house.
Didn't I put all this in original post?

not with adequate specifics -
how many hoses on your portable 1 ton air conditioner, and where is it taking the air from that it's heating and cooling? most I've seen have no hoses for the side that "conditions" air, and one for the side that exhausts hot air and evaporated water.
assuming yours is like the one pictured, where will you place the unit?


Originally Posted by oil pan 4 (Post 58708)
The dryer doesn't need to reuse it's own heat since it will be used in summer only, out in the garage where it will be 80 to 100F with 15 to 50% humidity.

The heat pump discharge will produce up to 18,000btu, if the dryer only uses 2/3 of that it's still over 3kw worth of heat.
If doing it this way makes the dryer take a little longer that's fine since it will be helping to cool the house.
This design goes against conventional design by actually helping cool the house. Every other design puts off heat.

it sounds like you're conflating the rate of heat production with energy consumed/released into the house. if that's not the case i apologize.

if you're venting a single-hose AC into the garage, you will be de-pressurising your house, and pressurizing the garage. this will lead to infiltration from the garage into the house, which is a bad practice. I assume you'd be ducting directly to the dryer and then the dryer to the outdoors? in that event you've built part of a recirculating heat pump dryer by virtue of depressurizing your house and bringing hotter, more humid outdoor air into the house to replace it, some of which through the hole you made into the attached (?) garage.

oil pan 4 04-17-18 04:46 PM

I put in the original post that the whole thing, which means the air conditioning unit and dryer are going out in the garage and that I was going to duct the cool air into the house and the hot air out of the garage.

I intentionally didn't specify if I was going to run open loop or closed loop. Because I don't know if I want to put 2 holes in the wall. But I will most likely run closed loop

I did not mention that the garage is an addition. It is completely sealed off with an exterior door and storm door and exterior stucco wall.
The garage is unfinished and very drafty. There will be virtually no pulling air pushing air from the garage to the house.

hazelp 04-18-18 04:27 AM


Your invention is Awesome. Is it available in the markets right now?
Best wishes

oil pan 4 04-18-18 08:45 AM

Yeah it's available.
You go buy a used electric dryer and a portable A/C unit with at least a single discharge duct for the hot exhaust and put them together.

hazelp 04-19-18 06:56 AM

Thanks for the info

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