Oversized and extreme high humidity

[Jeremy325]

I have a 15 ton J15P heatpump. This is a new jail engineered building. We are having a major humidity problems the unit runs only minutes until satisfied. This has a tandem compressor design. I believe the unit is oversized but getting some one to admit that is not going to happen!!! We are tring everything to help the customer. Do y'all have any suggestion. I though about unhooking stage 2, but I am worried about oil return because of velocity the lines are sized for a 15 ton. Thought about cutting hole in duct and dump above ceiling to see if helps do y'all have any recommendations thank you

[wdshea]

Lower the fan speed? I hope that wasnt insulting...

[Six]

You're going to either have to add load or remove capacity. It's sounds way oversized.

You could add duct heaters for reheat to increase space temp also.



There is a guy that reps a company that sells dehumidifiers here. He's pretty sharp too.

Maybe he'll chime in.

[wdshea]

Can you add a bypass to the conditioned space and connect the supply to the return?

Would that de-humidify "twice"?

[teddy bear]

I have a 15 ton J15P heatpump. This is a new jail engineered building. We are having a major humidity problems the unit runs only minutes until satisfied. This has a tandem compressor design. I believe the unit is oversized but getting some one to admit that is not going to happen!!! We are tring everything to help the customer. Do y'all have any suggestion. I though about unhooking stage 2, but I am worried about oil return because of velocity the lines are sized for a 15 ton. Thought about cutting hole in duct and dump above ceiling to see if helps do y'all have any recommendations thank you

First, you need a basic setup that involves balancing the air flow to max the amount of dehumidification that the a/c will do while maintaining the desire temp. Usually the coil air flow is too high and the coil temp is not low enough to provide the desire inside dew point. Assuming you want 75^F, 50%RH, (55^F dew point) your a/c coil temp should be <45^F. Also minimize your make-up air that is used. There are code minimums that you must supply. Supplemental dehumidification will be required during the low/no cooling load conditions. Also most of these types of facilities require fan "on" mode with required fresh air ventilation. If this is two speed a/c, both speeds must be balanced to maintain low coil temperatures.
After this setup is complete, calculating the amount of supplemental dehumidification is determined by the number of occupants, the amount of fresh air ventilation, and the desired indoor temp/%RH. 50-60%RH should be do-able. Avoid reheat because extreme high operating cost. The best dehumidifiers like the Ultra-Aire remove 6-7 lbs. of moisture per kw verses reheat which is <1 lb. per KW.
Keep us posted as these are learning experiences.
Regards TB

[Jeremy325]

Lower the fan speed? I hope that wasnt insulting...

Done that no change

[bigtime]

Keep the fan on low and lower the stat.

My home unit is oversized and cuts on/off a lot, but its not humid in my home.

IDK what the problem is, but prolly not an oversized unit. Maybe your jail is in a negative pressure? Thats what causes most humidity problems.

[Six]

First, you need a basic setup that involves balancing the air flow to max the amount of dehumidification that the a/c will do while maintaining the desire temp. Usually the coil air flow is too high and the coil temp is not low enough to provide the desire inside dew point. Assuming you want 75^F, 50%RH, (55^F dew point) your a/c coil temp should be <45^F. Also minimize your make-up air that is used. There are code minimums that you must supply. Supplemental dehumidification will be required during the low/no cooling load conditions. Also most of these types of facilities require fan "on" mode with required fresh air ventilation. If this is two speed a/c, both speeds must be balanced to maintain low coil temperatures.
After this setup is complete, calculating the amount of supplemental dehumidification is determined by the number of occupants, the amount of fresh air ventilation, and the desired indoor temp/%RH. 50-60%RH should be do-able. Avoid reheat because extreme high operating cost. The best dehumidifiers like the Ultra-Aire remove 6-7 lbs. of moisture per kw verses reheat which is <1 lb. per KW.
Keep us posted as these are learning experiences.
Regards TB

Avoid reheat because Ultra-Aire is the only solution.....

Ive got a surgical center with electric reheat in every OR room and a community building that runs a boiler for reheat.

IT IS an effective solution albiet expensive for controling humidity when a unit is oversized AND its been around for decades.

If its as oversized as he says it is and he's tried all of the tricks then the solution is most likely going to be expensive.

[bigtime]

Avoid reheat because Ultra-Aire is the only solution.....

Ive got a surgical center with electric reheat in every OR room and a community building that runs a boiler for reheat.

IT IS an effective solution albiet expensive for controling humidity when a unit is oversized AND its been around for decades.

If its as oversized as he says it is and he's tried all of the tricks then the solution is most likely going to be expensive.

Is there an OR anywhere without reheat? They need massive amounts of air to meet requirements. No way to move this much air and not have reheat to control humidity.

[Six]

I suspect there isn't but that wasn't the point of my post.

My point was that reheat is an option albeit expensive option for controlling humidity.

[chillerout1]

where is the stat located and is it a two stage stat? if it is oversized if you only run the first stage it should be ok. if if turns on then back off in a few minutes with only 1 stage that would mean that you are double what you need, unless somebody screwed up big time

[bigtime]

I suspect there isn't but that wasn't the point of my post.

My point was that reheat is an option albeit expensive option for controlling humidity.

Gotcha.

My point was that, imho, oversized units are not the cause of humidity problems. If they were, Id be soaking wet right now.

[teddy bear]

Without the correct setup of the air flow verses the coil temperature to assure dry air when system is operating, reheat or dehumidification is useless. Get to the 45^ coil temp, or a 30^F split, first before doing any dehumidification or reheat. Low coil temperatures also slow the cooling process which decreases sensible cooling capacity. This increases the run time. During high cooling loads days, most systems will handle the fresh make-up latent load.
Be my guest on the reheat verses supplemental dehumidication. Reheat is an energy pig, cosuming 5-10X more energy per lb. of moisture removed. During part load latent conditions, upto 2 lbs of moisture per ton of capacity most accumulate on the cooling coil to get moisture down the drain. Then at the end of the cooling cycle, the moisture on the coil/pan re-evaporates back into the space which makes it damp again. Ultra-Aires remove 8 lbs. of moisture per kw plus supply 11,000 btus per kw of free reheat to extend the a/c run. In some settings, the payback is less than a couple years.
Anyway, get the cold coil first.
If you are having trouble during high cooling loads, consider 70^F outdoor with rain. No cooling loads and high latent loads requires dehumidification in all settings.
Regards TB

[wdshea]

How does a colder coil slow the cooling process?

[teddy bear]

How does a colder coil slow the cooling process?

Colder coils reduce the btus per of cooling. Compressors pump less refrigerant at lower suction pressures.


Regards TB

[B1978]

I have witnessed humidity problems on fitness centers, lacking fresh air. You may be able to run one compressor fine without oil return problems.
Contact the manufacturer to verify. Also, have the manufacturer engineer a way to downsize the tonnage..
I would be concerned long term for that unit if it is that oversized.

[teddy bear]

I have witnessed humidity problems on fitness centers, lacking fresh air. You may be able to run one compressor fine without oil return problems.
Contact the manufacturer to verify. Also, have the manufacturer engineer a way to downsize the tonnage..
I would be concerned long term for that unit if it is that oversized.

There are many days where there is low/no cooling loads yet the outdoor dew points are above the acceptable indoor dew points. Plus the moistue the occupants add to the total moisture that must be removed. Over-cooling lowers the indoor temp which in turn increases the amount of moisture that must be removed to maintain low %RH. Supplemental dehumidification by high efficiency dehumidifier like the Ultra-Aire/Santa Fe/Hi-E Dry/Quest are a long term solution to provide ideal temp/%RH.
Regards TB

[B1978]

Could he add a ton of outside air to increase his load? Guess it depends on his region, whether he's in a humid area or not.

[ncboston]

If this is a new jail, are you at capacity yet? I would assume the engineers sized the unit based on maximum occupant capacity.

[Blows_Sucks_Heats_Cools]

The space needs to have positive pressure, but not too much. Make sure you have some make up air (approx 10%).

You need to run on 1 stage, cycling 2nd stage as needed. If you can control 2 stages of blower speed to go with your 2 stages of compressors, that would be ideal.