[EOppie]

Central FL area (humid subtropical). A family member is in a new construction home with a production builder. Blower Door result of 1.93. Originally, no fresh air intake, just a 100cfm bath fan in the attic.

After questioning, the builder added ventilating dehumidifier. However, the dehumidifier can't get below 60%, set to 45%. The heat pump is set at 78. The dehumidifier does not seem to be changing the humidity level in the house at all, despite running for over a week.

Installer says to use the Heat Pump to cool to 73 to dehumidify as the dehumidifier won't go below 60%. This doesn't seem right. The system is producing very little condensate.

What to check, or is this normal?

2k square foot home CMU Block, encapsulated spray foam attic, ductwork in conditioned space.

Broan B120DHV 120 Pint Dehumidifier

 

[Poodle Head Mikey]

I am presently due west of you on the Gulf. This house has all aluminum awning windows which provide excellent ventilation even when closed. <g> The house is 2' above sea level, has sunk, sits in a kind of lawn-bowl, and is damp as a natural rule. But without AC running a 30 pint dehumidifier is maintaining 49% RH as we speak.

Oh wait; I turned on the AC last night because my bed seemed too warm - still; unlikely the AC has run yet because it's set to 76º, the roof is solar reflective bright white, and it's in the low seventies outside.

My overall point being that it seems unlikely that your (400% larger than mine) dehumidifier can be working properly.

Something easy that you can do yourself is to catch the water from both the AC drain line and the dehumidifier drain line over a known period of time. Say; a half hour or 45 minutes, or an hour. Carefully measure the volume from each unit, in cups, and post your findings here.

PHM
------

Central FL area (humid subtropical). A family member is in a new construction home with a production builder. Blower Door result of 1.93. Originally, no fresh air intake, just a 100cfm bath fan in the attic.

After questioning, the builder added ventilating dehumidifier. However, the dehumidifier can't get below 60%, set to 45%. The heat pump is set at 78. The dehumidifier does not seem to be changing the humidity level in the house at all, despite running for over a week.

Installer says to use the Heat Pump to cool to 73 to dehumidify as the dehumidifier won't go below 60%. This doesn't seem right. The system is producing very little condensate.

What to check, or is this normal?

2k square foot home CMU Block, encapsulated spray foam attic, ductwork in conditioned space.

Broan B120DHV 120 Pint Dehumidifier

 

[EOppie]

Thank you PHM for the quick response, and for confirming that I think something is wonky. They turned the HVAC off as they are piped to the same condensate line, and placed a bucket under the drain to record what is generated. 79 F outside, 75 F inside
Humidity 59% inside, outside 65%

 

[kdean1]

At design temperature, a properly sized and adjusted air conditioner should achieve 75° and 50% RH. The system will run less when it is below design temperature so it won't dehumidify as much either. That is when the dehumidifier comes into play.

Measuring the condensate over a period of time is a good way to determine if the unit is working.

 

[EOppie]

The four-hour report: no condensate in the bowl

Indoor humidity is 61%, Indoor Temp 80

 

[kdean1]

The four-hour report: no condensate in the bowl

Indoor humidity is 61%, Indoor Temp 80

Was the trap primed at installation? If not, then it may be filling up. If yes, it seems your dehum isn't working.

 

[EOppie]

Was the trap primed at installation? If not, then it may be filling up. If yes, it seems your dehum isn't working.

Good question, but the dehum has been running for at least two weeks now, so unless it is a huge trap, I would have thought it would have filled by now. I will see if they can check the trap.

 

[teddy bear]

Central FL area (humid subtropical). A family member is in a new construction home with a production builder. Blower Door result of 1.93. Originally, no fresh air intake, just a 100cfm bath fan in the attic.

After questioning, the builder added ventilating dehumidifier. However, the dehumidifier can't get below 60%, set to 45%. The heat pump is set at 78. The dehumidifier does not seem to be changing the humidity level in the house at all, despite running for over a week.

Installer says to use the Heat Pump to cool to 73 to dehumidify as the dehumidifier won't go below 60%. This doesn't seem right. The system is producing very little condensate.

What to check, or is this normal?

2k square foot home CMU Block, encapsulated spray foam attic, ductwork in conditioned space.

Broan B120DHV 120 Pint Dehumidifier

As previously posted, the amount of condensate the a/c removes depends on the coil temperature verses the dew point of the air flowing through the coil. An example of this is wanting 75^F, 50%RH, a 55^F dew point, the a/c supply air dew point air must 5-7^F lower than the return air from the home. The supply air can be measured for to confirm the supply air temperature, %RH, and dew point. The dew point air must be 48-49^F dew point. The 5-6^F reduction amounts to about 3 lbs. of dehumidification per ton of cooling per hour during a steady run. To adjust, decrease/increase the air flow through the coil. This adjust is the starting point to gain control of the %RH in the home. Adding a dehumidifier to an a/c that is unable to maintain <50%RH will not work well because of the a/c and the dehumidifier be able to both participate in the maintenance of %RH in the home.

Next is the connection between the dehumidifier and the a/c system. The warm dry air of the dehumidifier must be introduced to the a/c system in a way that does not reduces the a/c systems removal of moisture when cooling. This means that the dry, warm dehumidifier air is introduced down stream of the cooling coil. This also warms the a/c supply air which will reduce condensation on the cold supply ducts.

This last point is that the dehumidifier should be connected to the air in the open part of the home without sucking warm dry air from the dehumidifier before the dry air goes through the home. This allows operating the dehumidifier when the a/c fan is off.

As previously mentioned, Checking the dehumidifier for function by measuring the in/out of the dehumidifier a reduction in dew point or moisture removed per hour to comform function.

Keep us posted on what you find.

Regards Teddy Bear

 

[Poodle Head Mikey]

Thanks.

Now turn off the dehumidifier at the circuit breaker and set the AC to control at about 75º F. - or four of five degrees below the room temperature.

After some water is actively flowing out of the condensate drain, place the water catchment container and start a timer. Check the volume collected in 15 minutes or 30 minutes - we can extrapolate.

Make sure the AC does Not shut off during the test period.

PHM
------

The four-hour report: no condensate in the bowl

Indoor humidity is 61%, Indoor Temp 80

 

[EOppie]

Thanks.

Now turn off the dehumidifier at the circuit breaker and set the AC to control at about 75º F. - or four of five degrees below the room temperature.

After some water is actively flowing out of the condensate drain, place the water catchment container and start a timer. Check the volume collected in 15 minutes or 30 minutes - we can extrapolate.

Make sure the AC does Not shut off during the test period.

PHM
------

So homework completed.

Ran the Heat Pump/AC and ensured it didn't shut off, the thermostat was set to 70. That cooled the house from 77 to 72 F. It took the indoor humidity from 59% to 55%. After water was flowing out of condensate drain we timed for 15min. It collected over 1 liter in that 15min time period.

Dehumidifer was shut off at the breaker.

 

[Poodle Head Mikey]

Well done.

How much over a liter? Way over? Or just barely over? <g>

Let's make it easy and project that it was about 120% of a liter because that is five cups. A cup of water weighs about 1/2 lb. So you collected 2 1/2 lbs of water in a quarter hour / 10 lbs. per hour. I forget the exact formula off the top of my head but I think it might be 3 lbs per hour per ton of cooling capacity being provided by a properly operating system.

So now: do you have a 2 1/2 ton AC system? If you don't know just post the model number of the outdoor unit. If the system is larger than than 2 1/2 tons you will likely benefit from having some talented someone reduce the indoor airflow. This will lower the cooling coil's operating temperature and increase the moisture removal. This will also slightly reduce the total cooling effect so it's somewhat of a delicate balancing act. As is the entire HVAC/R trade. <g>

Also: can you measure the temperature at an air return grille and also at the supply grille nearest the inside unit of your AC system? And if so; post them back here?

With your evidence of negative function now in-hand you should be demanding satisfaction from the dehumidifier-responsible party(s).

PHM
-------

So homework completed.

Ran the Heat Pump/AC and ensured it didn't shut off, the thermostat was set to 70. That cooled the house from 77 to 72 F. It took the indoor humidity from 59% to 55%. After water was flowing out of condensate drain we timed for 15min. It collected over 1 liter in that 15min time period.

 

[EOppie]

Well done.

How much over a liter? Way over? Or just barely over? <g>

Let's make it easy and project that it was about 120% of a liter because that is five cups. A cup of water weighs about 1/2 lb. So you collected 2 1/2 lbs of water in a quarter hour / 10 lbs. per hour. I forget the exact formula off the top of my head but I think it might be 3 lbs per hour per ton of cooling capacity being provided by a properly operating system.

So now: do you have a 2 1/2 ton AC system? If you don't know just post the model number of the outdoor unit. If the system is larger than than 2 1/2 tons you will likely benefit from having some talented someone reduce the indoor airflow. This will lower the cooling coil's operating temperature and increase the moisture removal. This will also slightly reduce the total cooling effect so it's somewhat of a delicate balancing act. As is the entire HVAC/R trade. <g>

Also: can you measure the temperature at an air return grille and also at the supply grille nearest the inside unit of your AC system? And if so; post them back here?

With your evidence of negative function now in-hand you should be demanding satisfaction from the dehumidifier-responsible party(s).

PHM
-------

Thank you!!!!

Model number on the unit is a carrier 25UNA836A320.

From my quick Google search it looks like that's a 3 ton system. I'll work on getting temperature readings.

 

[Poodle Head Mikey]

Oooppps! I see a mistake I made. It should say:

. . . you collected 2 1/2 lbs of water in a quarter hour / 10 lbs. per hour . . . a properly operating system should provide 3 lbs of condensate water per hour per ton of cooling capacity.

This is the mistake: 10 divided by 3 = 3 1/3 tons / not 2 1/2 tons.

So your existing system (apparently a 3 ton - based on the now-available model number) is actually slightly exceeding the standard moisture removal rate.

As a result my comments in regard to possibly reducing indoor airflow are not applicable to your circumstance. Please adjust your thinking accordingly.

But the above correction makes the central dehumidifier question even more important than previously as the failure to control indoor humidity is now 100% the fault of the non-functional dehumidifier.

PHM
-------

Well done.

How much over a liter? Way over? Or just barely over? <g>

Let's make it easy and project that it was about 120% of a liter because that is five cups. A cup of water weighs about 1/2 lb. So you collected 2 1/2 lbs of water in a quarter hour / 10 lbs. per hour. I forget the exact formula off the top of my head but I think it might be 3 lbs per hour per ton of cooling capacity being provided by a properly operating system.

So now: do you have a 2 1/2 ton AC system? If you don't know just post the model number of the outdoor unit. If the system is larger than than 2 1/2 tons you will likely benefit from having some talented someone reduce the indoor airflow. This will lower the cooling coil's operating temperature and increase the moisture removal. This will also slightly reduce the total cooling effect so it's somewhat of a delicate balancing act. As is the entire HVAC/R trade. <g>

Also: can you measure the temperature at an air return grille and also at the supply grille nearest the inside unit of your AC system? And if so; post them back here?

With your evidence of negative function now in-hand you should be demanding satisfaction from the dehumidifier-responsible party(s).

PHM
-------

 

[Poodle Head Mikey]

This mild weather - low/mid 80's - is not the design-temperature for your AC system. At the design ambient the system would be running 100% of the time. At lower temperature it adjusts it's cooling total capacity by turning off based on indoor temperature. When the AC is not running - it is not reducing the amount of moisture in the conditioned spaces. Which is exactly why you need the central dehumidifier - to control indoor RH in these shoulder-seasons.

 

[teddy bear]

Your a/c air flow needs to be slowed down. The 3 lbs. per hour per ton of cooling is at 50%RH. IN this case 55%-60%RH, we should of removed more moisture because of the higher indoor %RH.

Your are right about the dehumidifier not doing what it should. Two issues, is it connected to the home and a/c correctly and is it functioning?

Hopefully the house air passes through the dehumidifier and goes directly to the home. Passes through the home and returns to the dehumidifier. A 120 pint dehumidifier with 50%RH passing through the dehumidifier should remove 3-4 lbs. per hour. Pictures or rough drawings should confirm the connections. Measuring the temperature/%RH in and out of the dehumidifier plus measuring of the moisture removed should provide information on function.

YOU can see that this is a process of matching the load of the home to the a/c and dehumidifier.

Looking for more info.

Regards Teddy Bear