high humidity in my house

plumbergid · August 11

would anyone have answer to high humidity in chilled water high velocity system what can i do to get humidity from 65 to 45-50

Jamie Hall · August 11

Is that percent relative humidity? And at what space temperature? And how many air changes per hour?

The idea will be to get the dew point of the supply air low enough. If the air temperature is 70 and you want 45 percent relative humidity, you need to chill the air to below 48 F and then reheat it.

mattmia2 · August 11

Slow down the airflow to drop the supply air temp. How long are the cooling cycles? What is the supply and chill water temps?

HVACNUT · August 11

Air seal the house.

Oversized system?

Air handler in attic with leaky return ducts?

pecmsg · August 11

Chilled Water High Velocity system?

Make and model please.

plumbergid · August 11

this for Jamie

yes that is 65 RH

Space temp is at 72

i have an hrv that's doing 110 cfm for air change in a two level house with 1300 sq ft per level the HRV is dumping fresh air into the return 6 feet before the cooling coil and the HRV exhaust to outside is 3 feet before the fresh air also into the return air a hvac.

i had next to no condensation of off my chilled water coil until i cranked down my air flow through coil and dropped the chilled water temp to 32 degrees Fahrenheit (which is kind of low) i am reheating also but than the hvac is not quite keeping up what do you recommend i have the reheat temp it is a hydronic hot water coil

also i am afraid i am putting excess moisture into my ducts and creating mold with reheat is that possible?

plumbergid · August 11

this for HVACNUT

It is a new house and to my opinion very tight house

as for oversized i am not sure but i know my basement needs next to no air conditioning so when the chilled water is going the basement damper is closed it is a vfd operated hi-velocity system which claim you want 1100 to 1200 fpm per minute out of every diffuser in the house which is in my opinion to high (but not scared to be proven wrong)i have it cranked back to 950 fpm and than can bring the RH down only to 55-58 so wondering what you mean with oversized could that be an issue?

Jamie Hall · August 11

Not in a position to run all the numbers right now, but that HRV isn't helping you a bit. Consider: all the moisture it is bringing in from outside gets into your inside air unless it is taken out on the cooling coils.

You want to crank that chiller coil as low as it can safely go — and since it is water, 32 is it. Then crank up the air flow in the return (not the HRV) and the chiller power to run as much air as you can to get a discharge air temperature from the coil not higher than 40 (lower will be better)..

mattmia2 · August 11

i believe an erv would bring in less moisture, the hrv is making it so you're essentially trying to remove the latent heat from outside.

Jamie Hall · August 11

https://forum.heatinghelp.com/discussion/comment/1862216#Comment_1862216

This is true — but in a colder season, the latent heat recovery benefit of an ERV is more than offset by the potential for poorer (maybe much poorer) indoor air quality, and you can't just switch the operating mode from one to the other — they are very different beasts.

plumbergid · August 13

sorry for the late reply i am also farming and with that being the season kind of my second priority is plumbing

i am a bit confused because the hvac tech im working with thinks i need a bigger HRV and have it going full out also he thinks speeding up the air flow through the coil will absolutely help and he wants me to put water temp back to 40 -45 degrees i know that lowering helps get it down would you know what he is thinking and why he would say opposite than you guys

also wondering if the Freon level in condenser could have effect on humidity i have heard if it is low it could cause high humidity i cant really see that happening because it is cooling the water through a plate exchanger but ive heard it more than once we have a primary loop that loops the chilled water through a plate exchanger and the condenser cools the water then the primary pump pumps it into a buffer tank and then the secondary loop feeds it to my hvac cooling coil.

also some people have told me to keep my fan on auto in cooling mode instead of the on what is your opinion of that ?

also a big thank you to people who take the time to try and help me it is greatly appreciated.

Jamie Hall · August 13

I don't think a bigger HRV is going to help, unless you are in a dry climate. It would cool the incoming air, true — but in doing so it will increase the relative humidity of that air. If your outdoor relative humidity is less than about 20%, then it would help — but I doubt very much if that is the case (that's high desert humidity levels).

A coil outlet air temperature of 40 or so is cool enough for your purposes. What you need to do is run the fan as hard as you can, but not to exceed that outlet air temperature, and run the chiller full out.

ratio · August 13

To dehumidify with DX cooling, you need the air moving across a surface (the coil) that's below the dew point. To increase the moisture removal, you need to slow down the air, lower the coil temp, or both. What is the water entering & leaving temps now? What was it when you had the entering water cranked down to 32°?

With 32° entering water that unit should've been p!ssing like a racehorse, but if there's not enough water flow to keep the whole coil cold, it ain't gonna work so well. Similarly, if the air flow is too high, it's not going to remove very much moisture either.

You're going to have to take some measurements to find out what's going on.

bburd · August 13

The indoor fan should be off when there is no call for cooling. If it continues to run, when the cooling coil warms up the moisture condensed on it will re-evaporate back into the supply air.

Leave the fan in "auto".

EBEBRATT-Ed · August 13

We need Chilled water temp in and out of coil and air temp in and out of coil. 38 degree water inlet should get you to 50% rh.

What is the rated capacity of the system?.

It, not to hard to figure out the problem with the right information. Agree with @ratio

pecmsg · August 13

chilled water is generally 42-46*f

That is poor for humidity control.
get a whole house dehumidifier with outside air hookup.

plumbergid · August 14

would a regular water thermometer work or do i need something special for air?

mattmia2 · August 15

nothing special, something like a kitchen probe thermometer will do.

EBEBRATT-Ed · August 15

If the system will not remove enough humidity:

it could be one of the following

CW not cold enough
Air flow. Lower airflow will remove more humidity but you also have to have enough airflow to handle the sensible load and latent load
dirty filters
dirty coil
coil not large enough may be ok for sensible load but a thicker coil removes more humidity all other things being equal
coil in and out water temps and air temps in and out of coil will tell the story.

plumbergid · August 15

thank you Ed for your help

Can you explain what you mean with your second comment because it is a high velocity system that is designed to put out 1200 fpm per defuser and I've got it down to 950 fpm wondering if that is an issue, the cooling is running longer but is still satisfying the cooling calls i am in the process of trying to get those temperatures but don't have the right tools.

Jamie Hall · August 15

Um. Well, follow @EBEBRATT-Ed adivce. But don't confuse velocity with volume. You need to move all the air you can across those coils, because that's where the moisture is removed. And that's volume — velocity times area.

high humidity in my house

Comments

Categories