Desiccant Wheel

[the good doctor]

I am looking for some information on a good Desiccant Wheel to help remove mositure from a testing lab here in Minnesota. We are having trouble keep a handle on the humidity level in the summer months. We have three chillers along with three steam boilers that run year round. I am working on changing the program (energy management) to open the heating valves before the cooling coil to help remove so moisture; but is taking a lot of energy and not able to keep a handle on the system yet. This building runs 24/7 so you would think that one could get in the ballpark. But the levels bounce all the up to 75% on a rainy day! Any info would be very much welcomed. GD

[cxagent]

ASHRAE's book Humidity Control Design Guide is a good place to start. I can't recommend that book highly enough. For desiccant manufacturers, try Munters & Bry-Aire. There are probably more but those are the ones I have seen.

Be warned, desicant wheels as energy recovery ventilators (ERV) will do little to help your situation. Those are actually "load reduction devices" instead of humidity control devices.

[teddy bear]

Originally posted by the good doctor
I am looking for some information on a good Desiccant Wheel to help remove mositure from a testing lab here in Minnesota. We are having trouble keep a handle on the humidity level in the summer months. We have three chillers along with three steam boilers that run year round. I am working on changing the program (energy management) to open the heating valves before the cooling coil to help remove so moisture; but is taking a lot of energy and not able to keep a handle on the system yet. This building runs 24/7 so you would think that one could get in the ballpark. But the levels bounce all the up to 75% on a rainy day! Any info would be very much welcomed. GD

Wheels work well when dry exhaust air is routed through the wheel with wet fresh air also routed through the wheel. 50% of the moisture transfers from the wet to dry air. Using reheat requires the heat tobe added down stream from the cooling coil. Also the water chiller must have very cold water to be effective. Also consider free standing dehumidification for short term solution. Look at the Hi-EDry 195 at thermastor.com. These units are used in water treatment plants throughout MN to maintain less than 55^F dew points. These dehumidifiers generate some reheat as part of the dehumidification process.

[ozone drone]

Munters makes a very high quality air handler and desiccant wheel system. At the museum where I work we have photography archival vaults where photos and negatives up to 150 years old are preserved. Humidty control is critical. One vault we keep at 30% and the other at 40% and have had very good success and reliability with the Munters equipment.

Contact them at their factory (Located in Amesbury MA) ask for Engineering/sales 978-241-1100

[jchilling]

Shameless plug: Visit http://www.semcoinc.com and click on "desiccant wheel products". Cxagent is correct as concerns energy recovery ventilators, however, we have a complete line of custom air handlers that incorporate our desiccant wheels. We also sell just the wheel as well if you are looking to incorporate it into your existing system.

[cxagent]

Originally posted by cxagent

Be warned, desicant wheels as energy recovery ventilators (ERV) will do little to help your situation. Those are actually "load reduction devices" instead of humidity control devices.

I probably should have explained a little bit more. When the desiccant wheel is used to 'passively' recover energy from the exhaust air, it will transfer sensible and latent heat in the right direction to help reduce the heating/cooling load. However, it requires one of the streams (exhaust or intake) to be dry in order to reduce the moisture load in the building. If both streams are wet, the desiccant can't get rid of the moisture anywhere so it doesn't reduce the moisture in the building.

A desiccant wheel with 'active regeneration' (gas or electric heat) can remove moisture very, very effectively. This takes energy to regenerate (dry) the wheel after it has absorbed moisture out of the building.

Unfortunately, I keep seeing passive desiccant wheels installed and expected keep the building dry in all conditions. Once both indoors and outdoor air is wet the desiccant is loaded with moisture and moisture removal stops.

[jchilling]

Absolutely true. At the risk of being frowned upon for doing too much advertising, let me just mention that SEMCO has a product called the "Pinnacle" which utilizes a dual wheel configuration in which the second wheel is a "passive dehumidification wheel" (it does not require any additional heat source like the active dehum wheels). This unit can provide outdoor air at a humidity level of 40 - 45 gr/lb using standard cooling equipment even under a partial load condition such as the good doctor describes (e.g. 85 db at 130 gr/lb). In MN I doubt that there are too many of those days anyway......

Cx - you are obviously knowledgeable in this area, it might be of interest to you to have a look at this unit. Certainly any feedback would be welcomed. The most detailed description of this technology is here:

http://www.semcoinc.com/website.nsf/Downloads
Choose "Browse by product"
Then "Desiccant Wheel Products"

(I apologize for the huge list of literature, the piece to look for is titled "Pinnacle Series Technical Guide".)

[cxagent]

Originally posted by the good doctor
I am working on changing the program (energy management) to open the heating valves before the cooling coil to help remove so moisture; but is taking a lot of energy and not able to keep a handle on the system yet. GD

Doctor -

After rereading your post I have a question - Does the quote above mean that the heating valves open at an earlier time (before) the cooling coil? Or does it mean the heating valves open on a PREheat coil (air enters the preheat coil before the cooling cooling coil)?

jchilling - thanks for the info. I didn't mean to exclude or slight Semco in any way. I just named two companies that came to mind first.

[Carnak]

Originally posted by the good doctor
I am looking for some information on a good Desiccant Wheel to help remove mositure from a testing lab here in Minnesota. We are having trouble keep a handle on the humidity level in the summer months. We have three chillers along with three steam boilers that run year round. I am working on changing the program (energy management) to open the heating valves before the cooling coil to help remove so moisture; but is taking a lot of energy and not able to keep a handle on the system yet. This building runs 24/7 so you would think that one could get in the ballpark. But the levels bounce all the up to 75% on a rainy day! Any info would be very much welcomed. GD

When you are dehumidifying you want to reheat the air after it leaves the cooling coil. Hopefully your heating coil is down stream of your cooling coil.

The type of dessicant wheel you want would most likely be gas fired. The wheel would extract moisture from room then gets heated to drive out the moisture.

People suggested Munters and Semco which are good sources. If you want some one good try http://www.masongrant.com and ask for Lew. He wrote most of the ASHRAE humidity control design guide. Tell him some guy from the Caymans mentioned him.

I did a lab in Ontario. We had a custom packaged unit that over cooled air to dry it out, then had modulating gas heat to reheat the air.

This lab was under positive pressure, and with all the outside air used, it required a special "Dri-Steem" humidifier in the winter to keep RH up.

[sonc]

Originally posted by ozone drone
Munters makes a very high quality air handler and desiccant wheel system. At the museum where I work we have photography archival vaults where photos and negatives up to 150 years old are preserved. Humidty control is critical. One vault we keep at 30% and the other at 40% and have had very good success and reliability with the Munters equipment.

Contact them at their factory (Located in Amesbury MA) ask for Engineering/sales 978-241-1100
Munters rocks... if you need air drier than a popcorn fart...it's the way to go..I have pic's to back it up..

[ts ac tech]

Originally posted by ozone drone
Munters makes a very high quality air handler and desiccant wheel system. At the museum where I work we have photography archival vaults where photos and negatives up to 150 years old are preserved. Humidty control is critical. One vault we keep at 30% and the other at 40% and have had very good success and reliability with the Munters equipment.

Contact them at their factory (Located in Amesbury MA) ask for Engineering/sales 978-241-1100


Hey ozone drone...I too am responsible for two archival photograph vaults. And I have four Munters, two in each vault, designed as redundant/lead/lag systems. I have never seen them work properly because the condensation builds up so quickly inside the unit, it actually rains on the circuit board and fries the board withing hours of operation. As a result, I have portable space dehumidifiers doing the job instead. I would be very interested in putting our heads together to come up with a solution.

[jchilling]

Cxagent - I didn't feel slighted in the least. I know that other companies come to mind first and I'd like to try and change that. I got a little carried away here and was too aggressive in my post.....

Munters makes an excellent system also, no doubt about it.

[coolh2o]

The best type of equipment for this application sounds like "liquid desiccant". See http://kathabar.com I have used these systems in surgical suite applications, food processing and pharmecutical plants. They are available in a wide range of sizes and are very effective. The ability of liquid desiccant to remove water vapor from air or add water vapor to air is determined by the temperature and concentration of the solution. Depending on the concentration, the conditioner delivers air at any desired relative humidity between 20% and 90%. This system allows air to be delivered at the required temperature and humidity regardless of air inlet conditions.

[the good doctor]

I want to thank all of you for your valuable info. I agree with you that the heating coil should best be after the cooling coil to help drop the moisture content. I was not lucky enought to have my system set up that way. But what I am trying to do is pull the moisture that the outside air has been introducing to my building. Also, with a return air of 55 degrees and an outside temp this morning of 57 the cooling valve does not have much of a load on it. But by heating the air it forces the cooling valve open to help remove more condensate/mositure. So,its not a perfect system, but we are trying to do the best with what we have.
GD

[ozone drone]

[i]Originally posted by ts ac tech [/

Hey ozone drone...I too am responsible for two archival photograph vaults. And I have four Munters, two in each vault, designed as redundant/lead/lag systems. I have never seen them work properly because the condensation builds up so quickly inside the unit, it actually rains on the circuit board and fries the board withing hours of operation. As a result, I have portable space dehumidifiers doing the job instead. I would be very interested in putting our heads together to come up with a solution. [/B]

ac tech

At what temperatures are you keeping your vaults? we keep one at 20 degrees @ 30% rh and the other at 60 degrees @ 40% rh. I've noticed some condensate on the return air housings...but other than that no problems.

Are you familiar with the "Pre Dry" Procedure? When we were first commisioning and testing the systems, we found a problem with our cooling coils icing up. We solved the problem by "pre drying" the wheels before enabling the cooling.

All the procedure consists of is removing the fuses for the supply fan motor and running the desiccant wheels with the reactivation fan and heater on for about 45 minutes. If your wheels were idle for any length of time before starting the system, they become saturated and unable to get a handle on the load. By pre drying the wheels, they start off ready to get rid of the moisture.

My work # is 817-989-5129 (direct line) I'll give you my work e-mail address and we can see if I can be of any help.

[Edited by ozone drone on 08-10-2004 at 10:25 AM]

[bigmike]

good doctor,
It appears to me that while you are trying to remove moisture, you probably are not doing it. To remove moisture by cooling, you must cool the air down to or below its dewpoint to acheive condensation on the cooling coil. The air is then reheated to avoid subcooling the space. Unless I am missing something, all you are doing is heating the air up and then cooling it back down to its starting point. This will not remove any moisture. Changing temperature without reaching dewpoint will not affect the moisture content of the air. The desiccant systems work on a different principle so they can remove moisture without cooling.

I hope this helps.

[thermo]

You have a company in Owattona, Mn. that makes dissicant units.. website is CDI-HVAC.com I have used several on ice rink projects and find them very reliable..

[marauderx]

Also check out Semco, as they put out studies on microbial cross-contamination of their wheels vs. others, as well as variable frequency motor relations to air flow and optimizing economizer 'time' with running the wheel alone. Also they considered purge cycles and energy losses and effects on the overall system. They are great whether adding to your primary system or for dedicated OA.

It's good stuff.

[teddy bear]

Originally posted by the good doctor
I am looking for some information on a good Desiccant Wheel to help remove mositure from a testing lab here in Minnesota. We are having trouble keep a handle on the humidity level in the summer months. We have three chillers along with three steam boilers that run year round. I am working on changing the program (energy management) to open the heating valves before the cooling coil to help remove so moisture; but is taking a lot of energy and not able to keep a handle on the system yet. This building runs 24/7 so you would think that one could get in the ballpark. But the levels bounce all the up to 75% on a rainy day! Any info would be very much welcomed. GD

Desiccant Wheels are most practical when the desired dew point is near or below freezing because of ice formation on refrigerant dehumidifiers. The operating cost for +40^F dew points of Desiccant Wheel dehumidification is 2-3X more than the new high efficiency dehumidification system like Ultra-aire/Santa Fe or heat pipe assisted dehumidifiers. The investment for Desiccant Wheel is higher than hi eff dehus. is much higher.
For maintaining 75^F, <50%Rh, the "hi eff dehus" are the lowest investment and lowest operating cost.

[coolh2o]

Front end cost is higher but Kathabar Liquid Desiccant dehumidifier is the best across all temp. ranges and kills 94% of mold and bacteria.

[jchilling]

It would seem that the doctor has his homework ("due diligence") cut out for him.

I visited Kathabar's site. Interesting technology. I guess there's a lot of ways to "skin this cat" as it were.

It's unfortunate that the current system has been mis-designed or undersized in some way. Now doc is forced to make an investment in one of the above technologies in order to salvage the sizeable costs already sunk into this under-performing system. A desiccant wheel may be the most cost-effective means of reducing energy costs WHILE dehumidifying and also keeping this second initial investment in the "fix" low.

[Control Man]

MUNTERS does a great job , just be sure to size the cooling for the HI SUPPLY AIR temp coming off the wheel.

Just finished a MUNTER installation and with 122'F supply air the customer was happy when we oversized the chilled water coil and did not go with the engineers suggestion.

[sonc]

Originally posted by Control Man
MUNTERS does a great job , just be sure to size the cooling for the HI SUPPLY AIR temp coming off the wheel.

Just finished a MUNTER installation and with 122'F supply air the customer was happy when we oversized the chilled water coil and did not go with the engineers suggestion.

Did Reg do the start-up?