[Timber]

Need to lower the humidity in a cool room.

Must maintain 60 degrees for chocolate and RH between 45 and 55%.

Temp is OK but humidity is high, 78%.

Only way I know of is to install heat strips on back of evap coil and energize them when humidity is too high.Cut off when desired humidity level is reached.

Any other ideas, and where can I get the heat strips?

 

[westcoast refer man]

Timber,

Regarding other ideas- room humidity is a function of evap coil TD. The evap coil TD is the difference between saturated evap temp and desired room temp. A high TD will decrease humidity and low TD will increase humidity. If changing out your evap coils is an option (it may not be), contact your favorite refrigeration supplier and match up your evap size with the desired humidity.

 

[Timber]

Timber,

Regarding other ideas- room humidity is a function of evap coil TD. The evap coil TD is the difference between saturated evap temp and desired room temp. A high TD will decrease humidity and low TD will increase humidity. If changing out your evap coils is an option (it may not be), contact your favorite refrigeration supplier and match up your evap size with the desired humidity.

There are 4 fans on the coil, could 2 of them be cycled possibly in order to raise the TD.

I spoke with Krack, the manuf., and they suggested purchasing a 10 kw heater from Grainger, and control it w/ a humidistat.

 

[serviceman1]

Please correct me if I am wrong but I think that you want to lower your TD and your temperature and then if the temperature coming out of the coil is too cold for the application you should re-heat it.

 

[westcoast refer man]

Timber,

I suspect if you start cycling evap fans other problems may develop. Tevs work better when the air flow is constant and not changing. But, I have never tried that apparoach.

In the design work I've done, when humidity was an important issue, I've always selected the evap coil first, and then the condensing unit's requirements become obvious, ie required capacity at given evap temp.

I don't know why Krack is suggesting strip heat. Certainly, raising the room temp will lower the relative humidity, but how do you get the temperature back down where you need it? Unless your room is running too cold, and you could run it warmer, then I don't see how strip heat helps. You would have to take out alot of misture with your evap coil at a room temperature lower than what you really need, and then reheat.

Raising the room temp raises the relative humidity, but how does that help if your room temp is now too high. Its your evaporator that "wrings the moisture out of the air".

 

[Timber]

Timber,

I suspect if you start cycling evap fans other problems may develop. Tevs work better when the air flow is constant and not changing. But, I have never tried that apparoach.

In the design work I've done, when humidity was an important issue, I've always selected the evap coil first, and then the condensing unit's requirements become obvious, ie required capacity at given evap temp.

I don't know why Krack is suggesting strip heat. Certainly, raising the room temp will lower the relative humidity, but how do you get the temperature back down where you need it? Unless your room is running too cold, and you could run it warmer, then I don't see how strip heat helps. You would have to take out alot of misture with your evap coil at a room temperature lower than what you really need, and then reheat.

Raising the room temp raises the relative humidity, but how does that help if your room temp is now too high. Its your evaporator that "wrings the moisture out of the air".

Increasing the heat load will force the unit to cool, which in turn, will remove more moisture=(lower humidity).

Not very practical, but I have seen it work.

The unit is probably oversized. The ambient around this room can vary from probably about 60 to 80. That is not much heat gain since it is in a conditioned warehouse as opposed to being exposed to outdoor ambients.

Maybe as a test I could stick some space heaters in there and take some readings.

 

[teddy bear]

Need to lower the humidity in a cool room.

Must maintain 60 degrees for chocolate and RH between 45 and 55%.

Temp is OK but humidity is high, 78%.

Only way I know of is to install heat strips on back of evap coil and energize them when humidity is too high.Cut off when desired humidity level is reached.

Any other ideas, and where can I get the heat strips?

Dehumidification! Removes moisture while adding free reheat. Hi-E Dry 195 removes 8 # of moisture per and adds 12,000 btus per hour. The effect is the equeal to 12 kw of reheat and uses 1.5 kw per hour. Saves +10 KW and cost <three thousand and is the highest eff. dehu in the U.S. Check thermastor.com for above model.

 

[westcoast refer man]

Timber,

If your unit is oversized perhaps you could run it as if it was to reach a lower than normal temp. This will run the unit longer, wring out more moisture, and lower the RH.

Then the electric reheat can be used to raise the temp back up where you need it.

 

[gas-n-go]

im not sure if this will help you or not but we use a reclaim coil in order to maintain humidity in ac systems you could possibly do that, using heat from antoher system which is similiar to heat strips except more energy efficent. as long as you dont put too much heat too fast into your conditioned space your evap should be able to maintain propper box temp. i think heatstrips is perfectly aceptable means of doing what you need its just not energy efficent.

 

[codgy]

I don't believe that adding strip heat will solve your problem. The cause of this is the warm room temp of 60F and if you have conventional refrigeration coils where the normal TD is 10F, the coil temp never drops below dewpoint of the room. This means very little or no moisture removal. Check your condensate drains, I bet they are dry. I have used standard AC split systems for this application ( 3 phase with low ambient controls and lowered fan speed to assist w/ moisture control and maintain room temps of 62-65F with no controls to prevent coil icing. This setup has great reliability, cheap operation and low warehouse noise levels. I would use a ceiling fan to prevent air stratification if you have a tall warehouse.

 

[NormChris]

You need to cool, dehumidify and reheat. Here is my article on the concepts behind the process.

http://hvac-talk.com/vbb/showthread.php?threadid=33469

Norm

 

[sigma]

Norm, do you work for York or Bacharach?
Just curious.

 

[NormChris]

Norm, do you work for York or Bacharach?
Just curious.

I was a contract trainer for Bacharach for awhile. Now I am a senior training specialist for York on a fulltime basis. Plus, I write for the HVACR News and am publishing books with a technical publisher.

Still perform consulting services for Bacharach when they call me.

 

[sigma]

Now I am a senior training specialist for York on a fulltime basis.
[/B]

This is what I have red in last “HVAC Insider” but
I remembered your affiliation with Bacharach
and wasn’t sure.

 

[Timber]

im not sure if this will help you or not but we use a reclaim coil in order to maintain humidity in ac systems you could possibly do that, using heat from antoher system which is similiar to heat strips except more energy efficent. as long as you dont put too much heat too fast into your conditioned space your evap should be able to maintain propper box temp. i think heatstrips is perfectly aceptable means of doing what you need its just not energy efficent.

Krack engineer said the reheat electric heat strips could not be properly mounted on the coil that we have.Can they be mounted on the intake side of the coil? The fans are on the discharge side.

Model; sk-46-188a
Serial; 173974

Hmmmmmmm! Maybe Thermastor

 

[Carnak]

They need to reheat not preheat.

 

[Timber]

They need to reheat not preheat.

Another option would be to swap out the evap coil with a coil that has reheat.

 

[Carnak]

They need to reheat not preheat.

Another option would be to swap out the evap coil with a coil that has reheat.

I would say this would be the way to go, and the new evap coil would need a defrost system.

Mechanical dehumidifiers would end up frosting up in this temperature/humidity range as well, especially ones made primarily for human comfort conditions.

[Edited by Carnak on 01-12-2005 at 02:40 PM]

 

[eurothorbate]

I was having the same problem in the meat cooler in my business. I found that the easiest and cheapest way to remove the humidity form the cooler was to remove the humidity from the rest of my shop. For example, you are cleaning the shop and use hot water and you humidity is high, every time you open the door to your cooler you allow that extra humidity into the cooler. Therefore the humidity level never drops. Are your coils frozen all the time? If they are then you are extracting the most water out of the air with your setup. Try putting curtians on the doors to keep the humidity from getting in. This may allow the coils to pull the moisture out of the cooler. (cheep about $175 per door). If that doesn't work buy dehumidifier for the rest of you shop and drop you total humidity level. (I just use a cheep one from sears $325).
It just doesn't make sense to pay power to heat your cooler to pay power to cool it back out again. Better to heat your normally warm area of your shop. In the winter it is a bonus (drops your heating bill)

 

[rocket]

these rooms are normally designed at 20 deg TD
(i.e. a 12,000 btuh coil is a 24,000 coil at 20 TD)
this puts you in the ballpark, then you need to add dehumification

your coils are probably too big (10 TD)so
they need changing plus you need to get
dehumidfication equipt

you can try band aiding this stuuf, hope you get paid
for the limited results bad aiding gives. adjusting
your exitisting equipt

no coil mfr will size for 45% RH - there's a reason

remember, during off cycle no dehumification takes
place - probably 8 to 10 hrs in your case