RH Humidity Problems - Help!

[kayjh]

3000sqft in western canada. 4.5 tons combined capacity might still be on the big side. You should have seen some improvement however. But as mentioned, a 3 ton coil with a 1.5 ton condenser will result in a dry coil unless you really, really slow that blower down. I think a 2 ton coil is about as large as you want to go. I'd start by slowing the blower, but long term
you may need to put in a properly sized, matching air handler.

Also, 6CPH as mentioned is way too much. 2-3CPH is better for AC.

Thanks Motoguy (and everyone else taking the time to try and help). The 3T unit has a properly sized 3T condenser (I'm told). The 1.5T unit is new (Rheem) and I saw them install a new Rheem condenser. I'd be shocked if they mis sized it again. This is a bit maddening. Outdoor air temp is 23C today. At my office, when I arrived, indoor air temp is 23C/RH = 38%. When I left home the house was 22.5C/RH=59%. Both systems were cooling to the same exterior conditions and I used the same hygrometer to take the measurements. Not a professional tool though - a $20.00 unit from Home Depot.

[kayjh]

Allow me to shock U concerning some sizing realities in your climate toward controlling humidity.

I live in SW Wisconsin today 9/4/12 at 2-PM at Lancaster it was 90F & 54% RH; indoors it is 52% RH & 76F with good air circulation & totally comfortable.

Lancaster, WI very close to me, at 3-PM on the hour updates, it was 91-F; 50% RH; Heat Index: 97-F. NOW at 3:26 PM it's 50% RH in here on my first floor area & 76-F; around 25-C.

The indoor contains 45.7 gr/per/lb/air; outdoors 116 gr/per/lb/air; A/C has to remove 45.7 gr//per/lb/air to get to 52% humidity level indoors.

This is a 1937 farm home loaded with 13 windows on 1st floor &, NO shade until very late in the afternoon; first floor area 620-sf have a Half-Ton window shaker with an adjustable floor fan positioned to move air through all the rooms & back to the A/C.

Okay, 620-sf divided / by .5 (1/2-Ton) is 1240-sf per/ton of cooling.


3000-sf / 1240-sf per/ton of cooling is 2.4-Ton;

Well, U would have duct losses, etc., however, your home is way, way better insulated & protected from radiant & convection heat transfer than my home!

I have a Half-Ton on the 2nd floor which I only use in the evenings...

These small units have kept me perfectly comfortable in 112-F Heat Index.

How in the world could anyone 'initially' oversize equipment by that much?
Your home's calc should not be near where they had figuring it; even now it's still oversized for effectively controlling humidity plus meeting the sensible load.

I've never had a load calc performed on my home by me or anyone else; however, these light weight units do the job perfectly & use less wattage than most indoor blowers use!

It is amazing how much U can effectively cool with small tonnage; my all electric home monthly bills would shock your shoes off!

Udarrell,

I don't disagree with you. Sizing is a large piece of the puzzle. Prior to installation, I asked the HVAC company to do a Manual J and a Manual D. They had the wholesaler do the calculations, who told the HVAC company that 2 x 3T was needed. How a 4T air handler got installed, I don't know. After allot of time and discussion, it was revealed taht the wholesaler and misrepresented the tonnage needed and said the Manual J calls for 4.2T. So they put in the correct air handler (3T) to match the compressor for the LR unit and changed the bedroom wing to 1.5T. It was +28C when I got home from the lake this weekend and the house was +22C and the RH was 61%. It seems to me that the setup is wrong (air handler speed, cycles per hour, etc.) or I still have way too much cooling. This is a maddening process.

[kayjh]

I am posting the data of a properly setup ac supply and the effect on the space as the ac cycle. The critical issues are the air flow and the length of the cooling cycles. It takes 20-30 mins. to load the a/c coil /pan and moisture to start driping to the drain. Also at the end of the cooling cycle, the moisture on the coil re-evaporates back to the home. Longer fewer cooling cycles helps. Colder coil helps.
Keep in mind as the cooling load declines, do not expect the a/c to maintain <50%RH. Supplemental dehumidification from a dehumidifier is required when the outside dew points are near or above the desire inside dew point and there is note enough cooling load.
Regards TB
Attachment 305461

If we increase the cycle time and decrease the coil temperature to improve dehumidification, won't we supply colder air to the room and shut the thermostat off from the cold air entering the room? In other words, how to you get increased run times with the existing equipment without over cooling the room? Is the suggestion that we still have too much capacity?

[udarrell]

Udarrell,
I don't disagree with you.
Sizing is a large piece of the puzzle. Prior to installation, I asked the HVAC company to do a Manual J and a Manual D. They had the wholesaler do the calculations, who told the HVAC company that 2 x 3T was needed. How a 4T air handler got installed, I don't know.

After allot of time and discussion, it was revealed that the wholesaler and misrepresented the tonnage needed and said the Manual J calls for 4.2T. So they put in the correct air handler (3T) to match the compressor for the LR unit and changed the bedroom wing to 1.5T.

It was +28C when I got home from the lake this weekend and the house was +22C and the RH was 61%. It seems to me that the setup is wrong (air handler speed, cycles per hour, etc.) or I still have way too much cooling.
This is a maddening process.

Well, what don't U agree with?

First, they set the CPH wrong, U want it to run with as few cycles as possible; air flow with a TXV metering device should be a low as it will safely operate.

My home setup proves U don't need as much tonnage as U think or, sometimes even what the J calc says; I'd wouldn't use the additives in your climate area.

Vancouver, in British Columbia; 2.5% summer design is 77F & 66F wet bulb or, around 63% RH. Victoria is only 73F & 62F wet bulb.

Madison, WI is 88F & 73F wet bulb or around 49% RH. My area may be even closer to 90F design. The higher outdoor temp in SW WI means more grains of moisture per lb of dry air...

I believe they may be able to make your units work, if not downsize until they do work.

However, also remember that U have to have enough furnace air flow capacity for heating requirements in your area.

[kayjh]

Well, what don't U agree with?

First, they set the CPH wrong, U want it to run with as few cycles as possible; air flow with a TXV metering device should be a low as it will safely operate.

My home setup proves U don't need as much tonnage as U think or, sometimes even what the J calc says; I'd wouldn't use the additives in your climate area.

Vancouver, in British Columbia; 2.5% summer design is 77F & 66F wet bulb or, around 63% RH. Victoria is only 73F & 62F wet bulb.

Madison, WI is 88F & 73F wet bulb or around 49% RH. My area may be even closer to 90F design. The higher outdoor temp in SW WI means more grains of moisture per lb of dry air...

I believe they may be able to make your units work, if not downsize until they do work.

However, also remember that U have to have enough furnace air flow capacity for heating requirements in your area.

Airflow for heat isn't a problem. the house is heated with a hydronic system (baseboard radiant heat) that operates independently of the AC system. It sounds like the consensus is that I either have too much cooling, or mismatched equipment (still??). In addition, setting the 1.5T unit to cycle more is not helping the situation.

lately the house has been comfortable with 51% RH. I have the windows open and the AC off. The overnight temps are 16C so the house cools down nicely. I'd like to get the problems sorted out for next year though.

[bant]

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[motoguy128]

ECM motor will only help if a thermostat with dehumidification capability is connected and wired to the Air Handler control board to slow the blower for more latent capacity. ECM motor, at proper static pressures use less energy at all speeds, and use dramatically less energy at low speeds and static pressures. However, with undersized ductwork, they can actually use the same or even more energy than a PSC motor.

[teddy bear]

I may be mistaken, I thought your information regarding the solution done by you contractor included air handlers with ECM motors.
These motors were designed to give your home constant fan across the coil this should give you superior dehumidification with no more energy usage than your standard PSC motor in cycle mode. Even in the most humid climates, this option should work wonders on humidity.

Constant fan across the coil does not give superior dehumidification. Being able to slow the fan to the ideal air flow to provide a very cold coil without freezing gives better dehumidification.
When the t-stat is satisfied, the moisture that remains on the coil, usually about 1 lb. per ton of capacity re-evaporates back into the home. If the fan is off or "auto" cycle, this may take 1.5 hours. With fan "on" low speed drying the coil takes 45 mins.
When the outdoor dew points are +50^F, expect to need supplemental dehumidification to maintain <50%RH during low/no cooling loads.
Regards TB

[jpsmith1cm]

bant


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