I didn't want to hijack the other thread "Humidity out of control--help" as I don't have a crawl space but rather a usually normal RH basement.  New WF Envision 3ton startup was Aug 1st.  Unit has been running fine and I've been running with the fan on ON but just switched to AUTO tonight after reading the other Humidity tread.   I'm in the MetroDC area and when we had the August heat the house was set to 74 and while the temp is fine the RH is 60-65% both 1st and 2nd floors (have three electronic temp/RH units placed around)

The GSHP Installer's plumber was out last Friday and used a stick/numchuck looking instrument and would swing it around the one of the air-return ducts.  First was at 74degs and then again after the Stage-2 fan was on for 20 minutes.

What RH number should I expect?  I put in new efficient windows last winter so I don't think the AC runs as much but I keep it at 73-74 24/7 since Aug 1st.

Thanks for your help.

Chris

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Chris, I'm going to take the liberty of posting here what you emailed me via the site and then respond so that others may contribute or learn:


"... I just turned the Fan from ON to Auto. I put in new windows last winter so I don't think the house needs as much cooling as my old 18year York AC was putting out but I sure don't remember having this high of Humidity back in June/July with all the rain in the Washington DC area

The Installer's Master plumber came out last Friday to put a check valve on the cold supply to the desuperheater as I was getting a slug of hot when running cold when the AC had been running a lot. They think the the desuperheater pump could have been over powering the city water pressure.

While they were here they took two readings at the air intake. before and then again after 20 minutes of Stage-2. It was this tube looking thing kinda like a numchuck that they twirled around for several minutes and it gave a reading.

Seen anything like this? RH is 60-65%, I've got three electronic temp/humidity devices around the house to use and compare."



You may be a candidate for reducing CFM per ton so as to wring more water out of less air; shift the unit's sensible heat ratio away from sensible and toward latent heat removal (A 2 dollar phrase for dehumidification)

I don't understand the need for a check valve to prevent hot water backflowing into cold line. The only way for hot water to leave the hot water system is for some other water to replace the volume of water leaving, and I don't get how opening a cold tap makes that happen. Desuper pumps run at quite low head pressures, 1/10 or less of domestic water pressure. Maybe Bergy or Joe will have a different take on this from their greater practical experience.

I had to think a minute about your installer using nunchaku - I know parts of DC are crime-ridden...Actually he was using a sling psychrometer, an old school (and possibly more accurate) way of determining humidity. It's a thermometer with a wet cloth on the sensing bulb and in fast moving air (achieved by swinging) it'll cool to below the regular ('dry bulb') thermometer temperature in proportion to the air's dryness. Humidity is read by connecting dry and wet bulb temperature lines on a psychrometric chart.

You didn't say what humidity readings resulted from the nunchaku method and how they compared with your electronic instruments...let us know.

The plumber and helper did not share the results but told me they were taking them back to the owner to discuss. I'll see what the fan setting does in the next few days.  

Are there adjustments the installer can make to up the humidity control?  What disadvantage would this cause?

CH

They may not have known how to do anything other than record wet and dry bulb temps.

There is an easy accuracy test for electronic humidity instruments known as a salt test. This is from cigarsinternational.com:

"Try the Salt Test:
Luckily, as nature would have it, when salt and water (NaCl and H2O for you studious types), are in a saturated solution at equilibrium, the resultant humidity is 75%. This gives a fantastic reference point to calibrate our hygrometer. There is an easy way to determine if your hygrometer is accurate. Here's the procedure you should use: you need a ziploc bag, a screw-on beer bottle cap (or other small container) a small amount of salt (regular 'ole table salt), and water.

1. Place the salt in the bottle cap (or other small container).
2. Dampen the salt with water. Do not put so much in that the salt gets "sloppy". You want a damp pile of salt in the bottle cap.
3. Place both the hygrometer and the bottle cap full of damp salt in the ziploc bag and seal it well. (It is important not to let air on or out while the test is going on.)
4. Keep it like this for over 8 hours.

After 8 hours in the damp salt environment, the actual humidity inside the bag will be 75%. Compare it to your hygrometer, your hygrometer should also read 75%. If not, you will then know exactly how far off your hygrometer is. If it's off, note the amount and direction that it actually reads and be sure to add or subtract that amount when reading the hygrometer. If the hygrometer has a control to adjust it (either the needle or the display), you can set the hygrometer to 75% immediately after the test.

You should salt test your hygrometer every 6 months or so to be sure of the accuracy"

(end of text from cigarsinternational.com)


Cigar aficionados need to store them in an environment of carefully regulated humidity so they have a need for accurate hygrometers. I see no reason why the foregoing couldn't work with room humidity instruments.

I tested a couple Radio Shack units I owned ahile back and found them to read 10% high, and that was in keeping with how I believed they were reading, as well

Reducing fan speed (blower CFM) mean more water is removed from less air. There is a slight hit to both efficiency and total system capacity.