Proportional control, Zoning and Forced Air

Mike T., Swampeast MO

I don't like digital control. I don't particularly care for forced air either. Here's why...

I zoned my house for forced air cooling. Three zones: downstairs, master suite, and bedrooms; each with separate systems.

Master suite cools one bedroom, a study, a sleeping porch (sun room), master bath, walk-through closet and a 2nd bath.

When I designed the ductwork for this "zone" I intentionally planned for the bedroom and master bath to stay about 3° cooler than the rest of the space.

The master bedroom was designed this way because I, like many, do prefer to sleep in a rather cool space and it seemed wasteful to keep all the space that cool all of the time. The thermostat is in the bedroom.

The bedroom and sleeping porch are separated by a pair of pocket 15-lite doors. They were intended to be closed during the day and open at night.

I had to consider how the windows would be covered--it made a particular difference in the sleeping porch with eight large windows, 3 west and 5 north. The sleeping porch was designed to stay warmer in the day with the west shades pulled, but north open (love that north sunlight). It still took LOTS of cooling for the sleeping porch. So, the plan was to open those sliding doors at night to keep the sleeping porch from getting TOO cool...

Master bath was kept cooler as well to compensate for the lack of return air when the door is closed and for added heat gain from showering/bathing as well as a hydronic towel warmer.

I had to consider occupancy and other additional loads--lighting, tv, stereo, etc. Since it was all designed as a space used primarily in the evening, I didn't add much in the way of occupancy loading--presuming most wouldn't occur the the highest heat of the day...

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Everything worked exactly as planned.

Great you say? NO!!!!

Why?

BECAUSE THINGS CHANGED!!!

I resumed a leave of absence and the "study" is now my "office" during the day. I'm perfectly comfortable working about about 79 degrees during the summer. But now the occupancy load was concentrated in a single room during the day: a body, a computer, a large monitor, and a large laser printer that uses a fan to keep its electronics cool even when the heat fuser is off on "power save."

The occupancy load added another degree to the temperature differential, so to keep my office around 79° degrees I had to set the thermostat at 75°.

I did EVERYTHING I could think of to change this balance: keeping the doors to the closet that link the office/bedroom open; carefully setting the dampers on the ceiling registers; I even removed the damper from the register in the office. No matter what I did, the BEST I could achieve was that 3° differential that I designed for in the first place--it seemed "locked" in...

That design that seemed a good way to achieve comfort while still saving a bit of energy was haunting me now and instead I was WASTING energy in at least the amount that I had planned to save. ARGGH!!!!!

This is the curse of DIGITAL design. You ARE locked in!!!

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Compare this with my PROPORTIONAL heating system.

The iron radiators in all of the rooms in the cooling "zone" each have their own thermostatic radiator valve. No matter how the individual rooms are used, what the sun is doing, or how much occupancy load, I can keep each space at whatever temperature I want REGARDLESS of the temperature in any of the rest of the spaces. The state of window coverings doesn't affect anything to any real degree (take note architects!).

Even with rapidly changing outdoor conditions the temperature fluctuation in EACH of those rooms is less than with STEADY outdoor conditions and the forced air cooling.

The radiators are oversized and operate at low temperature. There is sufficient "headroom" in the reset curve to allow RAPID recovery from setback. The ONLY time you can feel any draft is if you "crank" a radiator in a room that has been SEVERELY set back--and then you only feel it during the "temperature rise" phase.

I keep my office about 65° in the winter when the hydronic system is running. My desk and body are in plain view of the radiator--at an angle such that the radiator appears completely solid but convoluted to my body seated at the desk. That arrangement WASN'T just "luck". The furniture was INTENTIONALLY arranged for this. I am in PERFECT comfort at this temperature, and since I work at home, I'm not always wearing shoes--sometimes even sandals--in the dead of winter with unheated floors and 65° air temperature! I keep my four-speed ceiling fan running at the lowest speed and temperature stratification is essentially eliminated yet the fan is moving so slowly that I really am not aware of air movement. I frequently wear cotton sweaters in the winter--I always push the sleeves above my elbow when radiators are on.

Since the climate here is HIGHLY variable, I included electric resistance heat in the air conditioning system. For the SAME LEVEL OF COMFORT I have to keep the thermostat at 72° or so, it takes FOREVER to get reasonably steady in temperature after deep setback, and I ALWAYS wear shoes--no sandals! To keep my head from being MUCH warmer than my feet I have to turn the ceiling fan up a notch. Then I am HIGHLY aware of air movement and I have to keep my sweater sleeves down...

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To homeowners reading this: ASK FOR PROPORTIONAL CONTROL. It does NOT have to be particularly expensive with a hydronic system--it may well even cost significantly less than a digital system with lots of zones--but it will STILL be more comfortable AND efficient AND ADAPTABLE TO CHANGE IN USE, LIFESTYLE, AGE, WHATEVER!!!!!

To contractors reading this: OFFER PROPORTIONAL CONTROL. Your customers likely don't even know that it exists--or if they do they believe it reserved only for the truly rich! Your customers will believe you to be some kind of magician! Your system design may well be SIMPLIFIED!!!! You don't have to worry about "splitting hairs" to achieve balance--just common sense!