The Right Data Can Find The Right Solution


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When I started learning the house-as-system approach to building analysis, it was only natural I’d have to rethink what I thought were the best solutions to a wide range of problems.

Having spent most of my career in manufacturing or distribution, I had a wide range of predetermined solutions to problems in pretty much any type of building.

During the years I spent in distribution, we would teach dealers in Upstate New York to sell add-on humidifiers to solve a homeowner’s humidity problem during the winter.

You know, reduce static electricity, reduce or eliminate scratchy throats, stuffy noises, dry eyes, and other symptoms one might experience during the long, cold winters caused by low relative humidity.

We’d give dealer salespeople simple, memorable data points like, “the relative humidity level in Upstate New York during the winter is lower than the average relative humidity level in the Sahara Desert.”

Well, it’s interesting how I had to rethink this challenge after several years of using the house-as- system approach to analyzing a building. One client in particular brought this home for me.

At TAG Mechanical, we had installed a humidifier in their home about four years prior to my getting a call letting me know they didn’t think the humidifier was working correctly.

So, to their house I went, my car packed with a blower door, duct blaster, and other associated test equipment. I was determined to find out what was really going on.

I showed up on a cloudy, snowy day, introduced myself and let the homeowner know that TAG was committed to figuring out their problem. I gave them my short (if you know me, 20 minutes) description of all of the testing and analysis I was going to do so we would have enough information to really figure out why their humidity levels where so low.

And off I went.

About 90 minutes later, with lots of data now in hand, I packed my test equipment up and asked the homeowner if I could come back the next day after anlyzing my test results. They were very gracious and let me know they’d be glad to have me back as long as I could give them a solution.

Here’s what I found:

  1. The homeowner set back their furnace each night to 62 Deg F to conserve energy.
  2. The blower door reading indicated an infiltration rate twice what code required.
  3. The furnace was at least 50% larger than the heat loss required.
  4. The ductwork had a total leakage rate of 300 CFM and leakage to the outdoors of 200 CFM.
  5. The relative humidity level in the home during the testing was 15% with an outdoor temperature of 32 Deg F and indoor temperature of 68 Deg F.

Applying a few basic physics principles tells us what was happening.

First, hot always goes to cold. Second, high moisture always goes to low moisture.

Because the house was leaking so much air, it wasn’t able to hold any moisture generated in the home through normal daily activities (cooking, cleaning, showering, etc). A typical family of four will create 2-3 gallons of water vapor each day, and in this case it was all being lost to the outdoors, because the house was so leaky.

Second, because the furnace wasn’t operating at night due to the thermostat being set back, no moisture from the humidifier was getting into the house during the night.

Third, during the day, when the furnace did operate, the run times were so short the humidifier didn’t have a chance to operate long enough to put sufficient humidity into the air to help the family feel better in their home.

What are the solutions?

The best solution was to air seal the home, so it wouldn’t leak moisture from the inside to the outside. At the same time we wanted to right size the furnace, so we could extend the run times, helping to improve comfort throughout the entire house.

The other option we had was to change the humidifier out and install a fan powered humidifier, so it could operate without having the furnace operate. Not my preferred solution, but one that technically could solve the problem of the low humidity levels.

We were able to convince the homeowner to do air sealing and then right size the furnace. It was easy once we explained the cost savings they’d see from a more efficient furnace and explained what was really causing low humidity levels – a leaky home.

Customers really can make the wisest decisions if we apply and take the time to explain the house-as-system approach to figuring out problems and developing solutions. And they will be healthier, safer, and more comfortable.

Ellis Guiles

Posted In: Building Performance, Residential Buildings

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