high humidity in my house

plumbergid

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

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

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

Air seal the house.

Oversized system?

Air handler in attic with leaky return ducts?

pecmsg

Chilled Water High Velocity system?

Make and model please.

plumbergid

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

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

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

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

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

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

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

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

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

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

chilled water is generally 42-46*f

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

plumbergid

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

mattmia2

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

EBEBRATT-Ed

If the system will not remove enough humidity:

it could be one of the following

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

plumbergid

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

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.

pecmsg

Have you measured the Chilled Water Temperature in and out? Air temperature in and out?

plumbergid

YES I HAVE BORROWED A TOOL AND HAVE MEASURED THE FOLLOWING

Supply water is 39 degrees f

return water is 43.3f

air temp in is 69.1

air temp out is 48.6

so wandering what i do now with these number my humidity was around 65

Jamie Hall

Either increase your water flow to the coil — while maintaining the same inlet temperature — or decrease the air flow over the coil to drop the outlet air temperature. But the latter idea may not work well, as you will be getting better dehumidification, but of less air.

pecmsg

With chilled water I would like to see 10° rise in Supply water in out.

20° Air drop is fine.

Is this a new system?

Jamie Hall

Um…interesting, @pecmsg . And a little discouraging. That output air temperature which the OP quoted won't get the humidity down to where he wants it.

pecmsg

20* air drop is considered fine.
5* water increase is low. Get that to 10* and I think more RH removal.
we still don’t know the sizing, how often it cycles or what type of controls?

neilc

@pecmsg

slow the water down ?

pecmsg

from here I’d say yes but I’d take more readings first

ratio

The Δ on the water is fine for now. Slowing the water down without lowering the EWT will increase the LWT (we're cooling, not heating), & will increase the AWT, & cooling will decrease. Slowing the water down along with lowering the EWT will lower the AWT & increase cooling, but simply lowering the EWT without slowing it down will increase cooling (slightly) more. Plenty of time to chase efficiency (increasing the Δ) later, once things are doing what they should.

We might be looking in the wrong direction. How confident are you (OP) that there isn't an unaccounted-for high-latent load? Lot of pets? Aquarium? Have you tried turning off the HRV to see what happens to the RH? It's my understanding that an HRV keeps the moisture in the building, making the equipment sizing even more critical for dehumidification. Is this a constant thing, or does it roughly follow outside conditions (high indoor RH when it's rainy, less high when it's drier outside)?

But cranking the water temp down low will help, at least until we can figure out what's happening. Water temp down, air speed down too. Since we don't have to worry about freezeups like we would with DX cooling, I'd crank everything down as low as I could to see how much condensation I could get.

EBEBRATT-Ed

His #s are fine. That coil should be dumping condensate like a racehorse. The colder the coil the more water it will remove. A 5 degree rise in water temp will remove more RH than a 10 degree rise.

Is this machine handling the sensible temperature with no issues? It should be with 49 degree air out.

Is it possible that some return air is bypassing the coil?

The other thing (and I have no Idea about your duct system) is if you have a return air duct that is disconnected in an unconditioned space pulling in extra RH.

Or a supply duct disconnected will in an attic will force the unit to pull in outside air through building leaks.

pecmsg

we need more information for this puzzle

Harvey Ramer

Just To chime in here;

Here are the loads from your HRV

Sensible Load: 0.215 tons (or 43.06 Btu/min)
Latent Load: 0.803 tons (or 160.5 Btu/min)
Total Load: 1.052 tons (or 210.4 Btu/min)
Sensible Heat Ratio (SHR): 0.205

Get the model and make of your chilled water coil and we can look up the Sensible Heat Ratio of your coil. If you have the wrong coil you'll have a problem getting there.

Also possible you may have to add an enthalpy wheel to the HRV or run a whole house dehumidifier.

Harvey Ramer

Calculated at an outdoor Db of 93 and Dp of 72.

Harvey Ramer

Here are the engineering specs on the common M-series unico chilled water module.

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Harvey Ramer

https://unicosystem.com/wp-content/uploads/2024/05/Bulletin-20-020.3.pdf

plumbergid

HI-Velocity cooling module model #70-1050 bthu 34000 is the cooling coil

and to answers a few questions yes the rh somewhat follows outside humidity but i have cranked it back so it runs 10 minutes on and 50 minutes off return ducting runs in the floor joists between first basement and upper level it is a 2 year old system and the chillers supply 8 units like this one with a reverse return system for piping the cooling load is always satisfied and when i crank down the air it does bring down the rh to about 55 but runs longer i also have to mentions the builders did not do a good job with their bathroom exhaust fans they ducted them all together in one outgoing duct without dampers so i have figured out that in order for them to work i have to run both together to make them work.

i have asked this before i have heard (more than once) Freon levels in the condensers can create higher rh is this true?

thanks for all the advice i have learned alot.

Harvey Ramer

Freon levels in the condensor are irrevelant in this instance. It is all about coil temp, air flow, ventilation loads, and building loads.

You don't by any chance have the actual building loads for the space?

I checked on the coil you have. The manufacture has no usefull data on their website. Would you happen to know how many rows of tubing are in the coil, (width, maybe 4 to 6)? and how many fins per inch?

Another thing that needs to be checked is the HRV balance. It should have both an intake and an exhaust fan. They need to be balanced so you are not depressurizing the space and pulling in outside air through other locations. Like the bath fans. Typically, you will want to HRV balance to be neutral to slightly positive.

If you are not at the proper fpm air velocity at the outlets, you won't get proper air mixing. This can also lead to uneven cooling and humidity situation in the house. Hardly enough to cause what you are experiencing though.

plumbergid

thank you Harvey

the hrv has an option to do a self test of some kind and i can see the cfm for intake and exhaust and they are both within the 108 to 110 mark with the exhaust being one or two cfm lower.

the fpm i have now at the outlets is 950 fpm and the design was 1200 so am a little low but trying to put air through coil slower.

i don't know the building load but will find it and post it.

EBEBRATT-Ed

Your water temps are low enough. I would guess that with the system able to satisfy the sensible temp (thermostat) and not the latent load (humidity) that you need more coil a thicker coil.

Usually systems they are sized on a basis of 75-80% sensible and 20-25% latent as far as coil capacity goes, but that does not mean that is right on your job. Some adjustment of fan speed can close the gap especially with chilled water but the bottom line is if the coil doesn't have the SHR ratio correct for your job it will be a problem

DCContrarian

What is your outdoor temperature and humidity?