house Humidity

Snowmelt

went to a house the humidity was high like 65% do I just suggest a house humidifier ? any suggestions

ratio

Standing water in the basement? Oversized cooling equipment? Poor/non-existent vapor barrier? Uncovered aquariums? Roof leak? High occupancy load?

These are some of the reasons I've found high humidity, leaving out the industrial process concerns. A dehumidifier might take care of the humidity, but if there's a more serious problem hiding behind it, that won't go away on its own.

ChrisJ

Where was it this high? Living space? Basement? Both?

Are they using central cooling? If so, how many CFM per ton? Does it have a variable speed blower?

What was the dewpoint outside and was it typical for the area?

Snowmelt

there is a ductless 3 ton unit, which is slightly over sized but not a lot, vapor barrier might be an issue, no fish tank or roof leakage, I will say this in the winter the humidity is so low that the customer gets nose bleeds and the dog is scratching her self/ in winter there adding humidity in the rooms.

Snowmelt

central air is being used, humid is both basement and living space. but with this rain it maybe 70 in the home with60% humidity

GBart

Do a load calc, is it's over sized it will not control humidity, period, check the length of the cycles, when it's 95-100 out and high humidity it should not shut off. Also customers need to be informed that our equipment is designed to maintain temp, not pull down, if they are turning off at night, set back, etc, it will not control humidity. If they are turning it down below 74-72 it will raise humidity, not lower it.

ChrisJ

GBart said:

Do a load calc, is it's over sized it will not control humidity, period, check the length of the cycles, when it's 95-100 out and high humidity it should not shut off. Also customers need to be informed that our equipment is designed to maintain temp, not pull down, if they are turning off at night, set back, etc, it will not control humidity. If they are turning it down below 74-72 it will raise humidity, not lower it.

It's a ductless, aren't most if not all of those inverters?
Generally those seem to control humidity very well.

Also, turning it down below 74-72 raising humidity depends on the system. A DX coil with TXV or EEV will most certainly continue to dehumidify, pretty much even to the point of running the coil below freezing if return temps drop enough.

Snowmelt

I'm thinking since its a modulating condenser and air handler that the system is running to tight and not letting it take the humidity out of the house, I have 3 - 12,000 btu and 1 - 7,000 btu unit, I am going to assume they modulate to less then 1/2 of what they are rated at, I don't know the exact number. the only other factor is that it seems like 5 out of 7 days were getting hit with rain , keeping the humidity level high

ChrisJ

To me, it sounds like infiltration is high.
I have the same issue in my house, but my system seems to cope with it pretty good.

I'd say a whole house dehumidifier would fix it. But they don't come cheap.

Snowmelt

yea I know , that's what I am thinking. I do have a cheap thing I bought at wall mart to keep it 50% instead of 90%.

ChrisJ

I run a 50pt per day dehumidifier in my basement set to 40%.
It runs almost non-stop from the spring until the fall. It drains into a condensate pump which pumps it outside.

Without it, my basement and crawlspaces run 70-80%. With it, they stay hot all summer, but dry.

Based on how many times I emptied the bucket per day before I put the pump in, I believe it's removing around 5 gallons per day.

Leonard

I cool ~ 1200 of 1500 SF house with 20k BTU old window unit in southern NH. Bath and kitchen are closed off with a double sheet so no heat/humidity input from them.

At night lately Very humid mild temps outside, when I turn AC on I need to run AC on LOW fan speed to get house humidity down. Guess on low speed air spends more time in evaporator, gets colder,and condenses more water out.

When I run fan on HIGH the place can get cold , but I still feel humidity is high. Pump runs at constant fixed speed . ( pump runs continuously, does not cycle at either high/low fan speed)

GBart

ChrisJ said:

GBart said:

Do a load calc, is it's over sized it will not control humidity, period, check the length of the cycles, when it's 95-100 out and high humidity it should not shut off. Also customers need to be informed that our equipment is designed to maintain temp, not pull down, if they are turning off at night, set back, etc, it will not control humidity. If they are turning it down below 74-72 it will raise humidity, not lower it.

It's a ductless, aren't most if not all of those inverters?
Generally those seem to control humidity very well.

Also, turning it down below 74-72 raising humidity depends on the system. A DX coil with TXV or EEV will most certainly continue to dehumidify, pretty much even to the point of running the coil below freezing if return temps drop enough.

Setting the temps low raises humidity regardless of system according to Dr. Carriers Psychrometric chart. Some customers are insane with cranking it down.

Does the system have "dry mode"?

GBart

Make and model would be nice.

http://www.daikinac.com/content/residential/single-zone/quaternity/control-humidity/

GBart

There's other issues too, cooking, showering, etc etc, are they vented? is the dryer vented? only takes between four and six pints of water to raise the humidity level inside of 1,000 square feet from 15% to 60%.

Are they turning the system off at night? set back, opening doors windows?? sometimes you have be a detective and go beyond our equipment, it can only handle so much.

ChrisJ

GBart said:

ChrisJ said:

GBart said:

Do a load calc, is it's over sized it will not control humidity, period, check the length of the cycles, when it's 95-100 out and high humidity it should not shut off. Also customers need to be informed that our equipment is designed to maintain temp, not pull down, if they are turning off at night, set back, etc, it will not control humidity. If they are turning it down below 74-72 it will raise humidity, not lower it.

It's a ductless, aren't most if not all of those inverters?
Generally those seem to control humidity very well.

Also, turning it down below 74-72 raising humidity depends on the system. A DX coil with TXV or EEV will most certainly continue to dehumidify, pretty much even to the point of running the coil below freezing if return temps drop enough.

Setting the temps low raises humidity regardless of system according to Dr. Carriers Psychrometric chart. Some customers are insane with cranking it down.

Does the system have "dry mode"?

Please explain?

The temperature of the evaporator dictates the dew point and the dew point of the supply air dictates the RH of the space.

Lower coil temperature means lower relative humidity.

I've had my own 16 SEER system drop the dew point down to 42 degrees. That means the house was 66 degrees and the RH was 42%.

How do I know? I have thermometers and hydrometers all over as well as temperature probes in my return and supply ducts. I also run a freeze stat on the evaporator as well as have the thermostat set to shut it off if the supply temps hit 40 degrees.

As the load on the evaporator drops as does it's temperature because the TXV or EEV control flow based on superheat.

pecmsg

Snowmelt said:

there is a ductless 3 ton unit, which is slightly over sized but not a lot, vapor barrier might be an issue, no fish tank or roof leakage, I will say this in the winter the humidity is so low that the customer gets nose bleeds and the dog is scratching her self/ in winter there adding humidity in the rooms.

Then the house leaks.............

a lot!

Yes minis ramp up and down but still wont dehumidify if operating too low!

GBart

ChrisJ said:

GBart said:

ChrisJ said:

GBart said:

Do a load calc, is it's over sized it will not control humidity, period, check the length of the cycles, when it's 95-100 out and high humidity it should not shut off. Also customers need to be informed that our equipment is designed to maintain temp, not pull down, if they are turning off at night, set back, etc, it will not control humidity. If they are turning it down below 74-72 it will raise humidity, not lower it.

It's a ductless, aren't most if not all of those inverters?
Generally those seem to control humidity very well.

Also, turning it down below 74-72 raising humidity depends on the system. A DX coil with TXV or EEV will most certainly continue to dehumidify, pretty much even to the point of running the coil below freezing if return temps drop enough.

Setting the temps low raises humidity regardless of system according to Dr. Carriers Psychrometric chart. Some customers are insane with cranking it down.

Does the system have "dry mode"?

Please explain?

The temperature of the evaporator dictates the dew point and the dew point of the supply air dictates the RH of the space.

Lower coil temperature means lower relative humidity.

I've had my own 16 SEER system drop the dew point down to 42 degrees. That means the house was 66 degrees and the RH was 42%.

How do I know? I have thermometers and hydrometers all over as well as temperature probes in my return and supply ducts. I also run a freeze stat on the evaporator as well as have the thermostat set to shut it off if the supply temps hit 40 degrees.

As the load on the evaporator drops as does it's temperature because the TXV or EEV control flow based on superheat.

The temp of the evaporator and how saturated it is dictates how much dew you get on the surface and you won't get dew unless there is humidity in the air, however when you cool air you are also shrinking it and a cubic foot gets smaller so the grains of moisture get closer together and humidity goes up, the colder the air gets the more a cubic foot shrinks and it snowballs, when the air re enters the room it expands as it mixes and humidity drops. If the customer keeps cranking the temp down you get the final reheat, you will get a swamp.

You can't technically control humidity with cooling, we do to a degree, but in commercial applications the only way to do it and maintain set point is with reheat, whether it be hot water, steam, coils, electric heaters, or hot gas bypass.

When you heat the air it expands and the grains of moisture drop per cubic foot because they spread out. That's the law of physics and you can't change it.

ChrisJ

GBart said:

ChrisJ said:

GBart said:

ChrisJ said:

GBart said:

Do a load calc, is it's over sized it will not control humidity, period, check the length of the cycles, when it's 95-100 out and high humidity it should not shut off. Also customers need to be informed that our equipment is designed to maintain temp, not pull down, if they are turning off at night, set back, etc, it will not control humidity. If they are turning it down below 74-72 it will raise humidity, not lower it.

It's a ductless, aren't most if not all of those inverters?
Generally those seem to control humidity very well.

Also, turning it down below 74-72 raising humidity depends on the system. A DX coil with TXV or EEV will most certainly continue to dehumidify, pretty much even to the point of running the coil below freezing if return temps drop enough.

Setting the temps low raises humidity regardless of system according to Dr. Carriers Psychrometric chart. Some customers are insane with cranking it down.

Does the system have "dry mode"?

Please explain?

The temperature of the evaporator dictates the dew point and the dew point of the supply air dictates the RH of the space.

Lower coil temperature means lower relative humidity.

I've had my own 16 SEER system drop the dew point down to 42 degrees. That means the house was 66 degrees and the RH was 42%.

How do I know? I have thermometers and hydrometers all over as well as temperature probes in my return and supply ducts. I also run a freeze stat on the evaporator as well as have the thermostat set to shut it off if the supply temps hit 40 degrees.

As the load on the evaporator drops as does it's temperature because the TXV or EEV control flow based on superheat.

The temp of the evaporator and how saturated it is dictates how much dew you get on the surface and you won't get dew unless there is humidity in the air, however when you cool air you are also shrinking it and a cubic foot gets smaller so the grains of moisture get closer together and humidity goes up, the colder the air gets the more a cubic foot shrinks and it snowballs, when the air re enters the room it expands as it mixes and humidity drops. If the customer keeps cranking the temp down you get the final reheat, you will get a swamp.

You can't technically control humidity with cooling, we do to a degree, but in commercial applications the only way to do it and maintain set point is with reheat, whether it be hot water, steam, coils, electric heaters, or hot gas bypass.

When you heat the air it expands and the grains of moisture drop per cubic foot because they spread out. That's the law of physics and you can't change it.

Commercial and residential are totally different applications.

Residential generally doesn't have near the latent load of commercial and will have enough run time to cope with the humidity.

It also depends on the SHR of the evaporator / CFM of the system. The slower the air flow, the better it will deal with the latent load. Again, within reason. It's not going to work in a movie theater full of people especially when it's cool out.

I'm all for hot gas reheat, it's just not really needed in residential.

Overall, I believe we agree.
I just disagree that going below 72-74 will raise the RH. It may be true with some systems, but not all.

If I raise my set point up to 74 my RH will go up because the system will run less.

Leonard

Put more simply, at start of cooling , COLD air exiting evaporator is likely at ~ 100% relative humidity ( at least here in humid northeast) . So the colder it is, the less absolute water content it has (grains of water).

Then as it warms (when mixed with warm room air) it's RELATIVE humidity is reduced. So the colder the AC air is the lower room relative humidity can be.

Many things limit low temp of evaporator, but think it's mostly heat loading. So I put my AC on low fan, seems to work better.
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Potential problem with a dehumidifier is if room temp is already warm/comfortable I wonder as extra electrical power dissipated by it how much it will raise room temps over the day. I have that problem over the day from running computer and tv in a large room (~ 350 watts). To point of having to put AC on.