Spoiled Rotten for Summer Comfort
Imagine a spoiled child in the back seat of the car, fussing, pointing, and demanding to have whatever he wants on short notice. There are no good reasons for all the demands other than, “I get to choose when and how for me.”
Well, it’s confession time. That’s me when it comes to driving. I like to decide by the minute, which radio station, how loud, windows up or down, what temperature, dashboard air or floor air, seat reclined or upright and etc. I am very grateful for all those knobs, switches, and adjusters. I’m guessing the car designers knew there are many drivers like me that enjoy minute to minute choices for everything.
How do I make such impulsive decisions? Of course there is no pre-planned strategy. It’s simple common sense, or maybe I should call it comfort sense. We are born with it, and for many of us, we have a very narrow range of personal comfort. Move slightly out of this range, and our comfort sense will immediately try to return us to a more comfortable situation.
So the typical drive with me will likely have the windows down, since I love the outdoors. I may even run the heat a bit to compensate for a cool day. Of course really cold weather and the windows go up. Bright and sunny, back down. Loud traffic, up. Birds singing, down. Hot and humid in the summer, up. Riding with a salesman who found his aftershave on sale at Big Lots, all the windows are down and coincidentally seem to be broken and will not go back up!
My point is that I decide how much outside air I want based on common/comfort sense. The decision variables change so frequently in terms of temperature, humidity, noise, and pollutants (inside and out) that I continuously adjust.
Here’s an idea: What if we applied some common/comfort sense to the amount of outdoor air we allow into our home? We all know we need some new air from outside, but how much air should depend on the indoor needs and the outdoor conditions. This sounds logical, but we are not sitting at the kitchen window at all times with our finger on the up/down switch like we are in the car. We are more dependent on mechanical ventilation with some degree of automation.
This is where I get fussy. Call me spoiled, but I want to be able to set up my fresh air automation exactly the way I want it, and that includes a device that knows when and how much fresh air to bring in. In my opinion, automated controls for residential fresh air ventilation still have a few weaknesses for us to resolve.
I would like my automation to take the following into consideration:
- Volume – Are you aware of the true volume of outside air you are injecting into a home per day? (Note from my duct design class, just because you attached a six inch duct to bring in air, does not mean you are getting 100 cfm.)
- Quality – Fresh air is great, but it’s not all fresh. How can you avoid the worst air?
- Need – How much “fresh” do you really need? It’s not really free, so ideally you will allow just the right amount. Should every home require the same amount?
- Conditioning – A mandated standard says you need exactly 137.5 cubic feet per minute of outside air to keep your family from turning green. Do you have the equipment to condition this air when it’s not perfectly “fresh,” and the automation to coordinate the devices?
- Expense – Keep the whole system affordable. Considering both initial costs and the conditioning costs, have you considered the total cost for fresh air?
If you read my previous article, “Indiana Soup,” you will know that I like to keep track of the moisture load on our homes. My appreciation for this poorly understood science is the reason I am so fussy about ventilation, and especially the deficiencies in ventilation controls.
Do you know your moisture science? Let’s say a ventilation control allows me to interrupt outside air ventilation for high humidity, and the choices are 65 to 85 degree dew point. I choose 70 degree dew point lockout. If you have 150 cfm of 70 degree dew point air come into your home, and your goal inside your home is 75 degrees and 50% relative humidity (55 degree dew point inside), then you will bring in almost a half-gallon of water “load” in one hour.
As I quipped in my last article, so what? The air conditioner runs and we’re all fine, right?
Yes actually, a three ton AC could remove about a gallon of water per hour, if it is running non-stop. So as predicted by my load calculation, on a design summer day, I should be fine. But what if the outside air is only 70 to 75 degrees with a high dew point? Then you have little, if any, AC run time while your ventilation system keeps sucking in
more moisture every hour. In these conditions, you really need a whole house dehumidifier.
Earlier this month I was presenting my Moisture Science 101 training, and that morning the Indiana weather was perfect for the lesson. “Let’s look at the weather,” I directed the class. We all checked our weather app for the dew point.
From my favorite weather data site, www.weatherspark.com, you can see on this chart what we found. At 11AM, you can see a relatively low 78 degrees but a high dew point of 73 degrees! You’re in the comfort business. What would you recommend?
Some control theories suggest the following to help high humidity problems (with my comments in parenthesis):
- Strategy: Air conditioner controls with special dehumidification mode that, among other things, overcools by 2 or 3 degrees to increase AC run time. (When I set my “accurate to one tenth of a degree” thermostat to 75, that is what I expect it to be. I do not want a runaway stat deciding my home will be colder than my very personal, exact comfort setting.)
- Strategy: Read the indoor humidity and lockout the ventilation if the indoors is too humid. (Fine, but when conditions improve outside, I am going to miss the opportunity to bring in fresh, dryer air because my inside is too humid. I would rather read and react to both indoor and outdoor conditions.)
- Strategy: Use an ERV to ventilate. (An ERV is not a dehumidifier. True, they can take out a portion of the incoming moisture, but during most summer conditions in my region they result in a moisture increase.)
What do I suggest? Being the spoiled child that I am, I want to ventilate smart with some common/comfort sense. Imagine an electric car window for your home with smart automation. This opening in the home might sense both indoor and outdoor conditions, might even project how much AC run time we expect, and if anyone is home. When conditions are right, it would allow a reasonable amount of fresh air ventilation, reduce the amount when conditions are marginal, and shut-‘er-down when “fresh” turns to soup. Up, down, up a little, down a tad, closed for now. I don’t think we’re there yet with this common sense technology, but in the meantime, be a bit cautious with high dew point conditions.
Posted In: Building Performance
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