Wood Kiln dehumidifier?

[The MG Pony]

A friend of mine runs a mill shop for wood, he makes kabinets to kitchens, he gets alot of his wood from a friend of his who has a mill so lots of the wood is wet.

His Kiln thus far is electric run and he's been using home style dehumidifiers, the resualts are good but short lived as the units die off rather fast due to the internal heat.

I have a couple 6,000BTU units that I think could be built to run as a dehumidifier for his 8*8*20 Kiln. To start the temp inside the Kiln will be: (Will have to get this info again!).

My plan for ordering the parts was evap, condencer 1 (Inside duct to reheat the air) then Condencer 2, to finaly ensure it was well cooled liquid going back to the TXv.

Does any one have any tips or sujestions that would ensure good opperation? Will either R-134a or R-22 be sufficient for this opperation, most old dehumidifiers used R-500.

For the evap I was thinking of just using 3/8 made into a spiraled coil siting inside the duct then a standerd style condencer after it to reclaim the heat, then the condencing unit rather un-modified. I'll be using an oil seperatour to have minimum oil inside the system and keep it at the compressor!

[Peter_1]

I've made many wood killn dryers, even with ambient temperatures of 60°C (140°F)

[The MG Pony]

Ah K, any design tips or could you help steer me into the right direction? I'm still working on my first heat pump project! lol

[Peter_1]

You only need one condenser in the system, installed just after the evaporator.
This way, you can mount the unit on 4 wheels.
The evaporator was mounted vertical and the condensor horizontal above the compressor. This way, the compressor was in the cold stream of the outlet of the evaporator.
Use a gas with low high pressure (R134a)
We used R114 in the past for the high ambient temperatures I mentioned (Bitzer compressors)
Try to evaporate at 0°C and don't be afraid to condens relative high.
You will need separate heaters - we installed electrical heaters - for the first warming up of the room.
Once it's running, the compressor will maintain the temperature
Do you also want to dry oak?

[star882]

It sounds a lot like the operating conditions of a heat pump clothes dryer. You'll probably need a special compressor for good results. (You can also try a regular compressor and keep the superheat low.)

[US Iceman]

The equipment Peter is describing is all based on standard components I believe. The special areas are the engineering to make it work and how the system is put together.

The critical aspect of this is to keep the components within the design application envelope. The operating conditions may be non-standard, but the application of the components is basic.

[Peter_1]

Spot on US Iceman, the components are all standard ones.
Superheat can be held low by a controlled (TEV) injecting liquid in the suction, just before a suction accumulator (sorry NoNickName, liquid strainer:p )

Just if you wants to dry oak, then I suggest that you ask to coat the evaporator, especially the bends on the side where they're soldered or use a stainless steel one.

We've done it and it worked very well by spraying zinc on the bends ( http://www.zinga.be/ ) and repeated this twice a year (the customer did it himself) so that the zinc acts as a sacrifying metal and protects better the copper.

http://www.ca.uky.edu/agc/pubs/for/for55/for55.htm

[Abby Normal]

A friend of mine runs a mill shop for wood, he makes kabinets to kitchens, he gets alot of his wood from a friend of his who has a mill so lots of the wood is wet.

His Kiln thus far is electric run and he's been using home style dehumidifiers, the resualts are good but short lived as the units die off rather fast due to the internal heat.

I have a couple 6,000BTU units that I think could be built to run as a dehumidifier for his 8*8*20 Kiln. To start the temp inside the Kiln will be: (Will have to get this info again!).

My plan for ordering the parts was evap, condencer 1 (Inside duct to reheat the air) then Condencer 2, to finaly ensure it was well cooled liquid going back to the TXv.

Does any one have any tips or sujestions that would ensure good opperation? Will either R-134a or R-22 be sufficient for this opperation, most old dehumidifiers used R-500.

For the evap I was thinking of just using 3/8 made into a spiraled coil siting inside the duct then a standerd style condencer after it to reclaim the heat, then the condencing unit rather un-modified. I'll be using an oil seperatour to have minimum oil inside the system and keep it at the compressor!
Ventilate with that dry alberta air

[Peter_1]

MGPony,just re-read your post: an oil separator isn't needed at all.

You will have to install a finned evaporator, just a bare coil will not work (exchanging surface far too small)

I should take R134a, the room needs to run at +/- 40°C (104°F) so this will give you pressures of +/- 16 bar (230 psi) where this will be 22 bar (or 320 psi)

You need all the heat the machine can gives to maintain the needed high room temperature.

You doesn't need cool liquid to the TXV, just subcooled liquid.

This is in fact a very basic machine.

http://www.nigos.co.yu/nigolux8eng.html

We installed also additional fans inside the room to increase circulating air volume like this http://www.nigos.co.yu/conddryers.html

8*8*20 is how big in metric :confused:

R500 gave relative low high pressures, same reason why we used R114

[The MG Pony]

Ventilate with that dry alberta air

BC! Thank you. We most certainly don't have dry air!

[The MG Pony]

In SI 2.5M * 2.5M * 6.1M. I was orrigionaly going to have the compressor external to the air stream.

I have a 2 - 3 Ton scroll as well, set to origionaly use R-22, but with an oil change it may work out well.

[star882]

the room needs to run at +/- 40°C In that case, you should be able to use a standard condensing unit and evaporator and just slow down the evaporator fan.

[Abby Normal]

BC! Thank you. We most certainly don't have dry air!
Castlegar is pretty dry, Vancouver Island despite its proximity to the pacific probably would not have much more of a dewpoint than 60F as a worst case scenario

[Abby Normal]

winter time it's all dry

[The MG Pony]

if you call 85/95% humidity dry.

[Peter_1]

85% at -20°C is indeed dry but I know what you mean.

[The MG Pony]

Hmmm new one to me? then what do they call wet? 100% I think we're swimming at that point! lol

[Peter_1]

If you breath in that air and your mouth our your throat our lungs heats this up to 37°C, then this will dry out your mouth.

To place it in your example, if you take this cold but humid air and reheat it to the desired 40°C in your kiln dryer, then it will reuslt in an RV of +/- 5% and a very, very low absolute mositure content.

Perhaps this clarifies a little bit more what I was trying to say. , what I mean, numbers can be so relative.

Source: Regional average forecasts for Alberta which gave me a minimum temperature of -18°C

[The MG Pony]

But I am talking about BC, whats all this about alberta?

[Abby Normal]

The ALberta comments are my fault, that is where I thought you were from.

Relative humidity is the most confusing term in HVAC as it is relative to the temperature.

Example it could be a pea soup fog (100% Relative humidity) and the outdoor temperature was 10C . If you could warm this 'saturated air' to 24C, the relative humidity would have dropped from 100% to less than 42%, yet the amount of moisture in the air would be the same.

Get temps down to close or below freezing and the air holds very little moisture compared to room air temperature. Ventilating in winter lowers the RH indoors.

Because you are near the pacific does not make you humid.

Highest recorded dewpoints in the world are in the Persian Gulf

[The MG Pony]

Why I say it is humid as it takes any thing forever to dry via evapouration, at least at ambient temps.

Your example makes alot of sense after a good nights sleep!

[Steve Coates]

Hi,

I have been also asked to look at replacing a wood drying kiln dehumidifier. The old unit no longer works and is roughly 2ft x 1ft x 1ft in size. I was hoping to copy the old unit for sizes but the small hermetic compressor datails are not visible and the unit runs on R12. The condenser and evap are roughly 1ft x 1ft x 4inches. Can anyone give me some idea of compressor and capillary sizes for this unit if I was to use R134a?

[Gary]

When the ambient air is less than 0C, even at 100%RH, and heated to room temp (or higher), it will outperform a dehumidifier.

[glenn1340]

Here`s an interesting link if anyone needs a new dehumidifier www.humiditycontrol.co.uk/flexisorb.htm (http://www.humiditycontrol.co.uk/flexisorb.htm)

I`ve been doing some work on one recently, pretty simple idea but effective

[alex.wang]

Agree with your opinion