Indoor Air Quality - temp, humidity, and discomfort

[Poindexter]

We had a pretty good thread going about a year ago, but no one has posted in it since Nov 2023, so I am starting a new thread. Old thread: https://www.hearth.com/talk/threads...d-indoor-air-quality-hearth-com-style.198427/

Today I built a sling psychrometer to better understand what is going on in my living space and out on my lawn...

 

[Poindexter]

I used a cleaning patch for my rabbit rifle to hold the water up against the wet bulb. Took a dental tool to get it finagled in there, but I was about to do unspeakable things to some Qtips to harvest some cotton.

Anyroad the air inside my house is about 80dF and about 50-55% RH as measured by my new doohickey. Well outside the ASHRAE defined "comfort zone" on the psychrometric chart. There is a guy Tim DeStasio has a youtube channel, I find him to be concise in the "psychrometric Saturday" series of shorts.

Our local hot weather pattern has broken. Outdoor temp is about 60dF. It is raining. Measured on my front porch out of the rain, outdoor humidity is >95% per my sling psychrometer.

So, I know from drying firewood in kilns each 20 dF change in temperature will halve or double RH, with the fundamental understanding that hot air can carry more water vapor. So 60dF at 100% RH should have the same absolute humidity, the same grams of water per cubic meter as 80 dF air at 50% humidity. Low and behold the calculated dew point for my indoor air is 60dF.

I want that 60 degree air in my house, but I want to pull some (a LOT of) water out of it on the way in. Can an ERV do that if I yank my HRV and replace it with an ERV? Can there be a bypass on there so the air to air intercooler isn't preheating the incoming air?

I am also a bit disillusioned about the amount of heat my stand alone dehu releases into my living space. I looked at stand alone ducted AC units at Costco today. Seems to me to maximize efficiency the duct blowing hot air outdoors needs to be as short as possible, basically move the dryer out of the way and use a short duct to the dryer vent.

 

[stoveliker]

Mini split...
Dehumidification without heat input or ducts. And quieter than a stand alone dehumidifier

 

[EbS-P]

No way an ERV can pull that much moisture out. Ventilating dehumidifier is the correct solution. I’m of the opinion that any tightly sealed living space needs one.

So yes they heat the house. Any dehumidifier will. But when you take the whole year round efficiency it should be a wash. We have plenty of wet 55 degree days that the house needs a bit of heat. Thing is if you have a ducted HVAC system the hot air is spread out some and not just dumped in a single room. The vent closest to the unit will get more warm air. Commercially reheat is a thing run the ac to drop drop humidity then heat the air back up somehow. Not super efficient but let’s say you want humidity control in a movie theater in the fall. Run the ac dry the air out then burn some gas to warm it up.

Efficiency wise dehumidification is like push a rock up hill. So is air conditioning or heating. I don’t think it’s that big of a financially hit. A plot I will make for those down south. Reducing the humidity increases the sensible output of you AC equipment because less compressor energy is spent condensing water vapor on the coil.

A ventilating dehumidifier can be controlled with a co2 monitor to run the fan only. A damper on the fresh air intake can also be controlled based on indoor co2.

Air will be filtered by a filter at the unit inlet. Hepa filter could be used. The ultimate system would be one where the fan and fresh air damper are controlled to manage indoor co2 and a separate control maintains humidity. I don’t have fresh air nor do have have c02 controller. I’m guessing that that would have added $1500 to $5k-6k install.

This is really beyond any HVAC company that doesn’t specialize in high end homes. But they have the skills to install the equipment maybe just not understand why you want it set up that way.

 

[gthomas785]

Dehumidifiers do produce heat, and it's not just waste heat from the power being used. It's also the latent heat that's been removed from the moisture in the air.
If you want dehumidification and a dehumidifier warms the room too much, do use an air conditioner. You can use a dehumidifier and ac together to get the right temp/humidity balance. Don't bother with the portable AC units unless it's really a temporary thing. The single duct ones in particular are pretty wasteful because they pull conditioned air from the room to cool the condenser coil and blow it outside.
Mini splits are popular for a reason. They're pretty easy to retrofit on any house, they operate silently, they're highly efficient. If you don't want to drop the money for one of those, get a window unit.

 

[Pinesmoke]

I have to shut down my ERV this time of year. The passive dehumidification it has does nothing and spikes my RH inside. Even running it 5 min per hour adds 5-6%.

I'll get around to a whole house dehumidifier at some point. Running a 50 pint unit keeps me in the mid to high 40 RH

 

[EbS-P]

I have to shut down my ERV this time of year. The passive dehumidification it has does nothing and spikes my RH inside. Even running it 5 min per hour adds 5-6%.

I'll get around to a whole house dehumidifier at some point. Running a 50 pint unit keeps me in the mid to high 40 RH

Are you measuring indoor co2?

 

[Pinesmoke]

Are you measuring indoor co2?

No but I figure 50 trips through the door to the porch does a decent air change.

 

[EbS-P]

No but I figure 50 trips through the door to the porch does a decent air change.

We have 5 kids and a dog. When it’s humid, all the in and out worker dehumidifier. Highest CO2 is always in the morning.