Sophisticated or simple control when systems will not be used mu

Doug B

I'm designing a radiant heat system for a home in Colorado where there is not only plentiful sun energy but the house is built with Insulated Concrete Forms with an effective R-value of 50. A Thermomax solar panel will provide a heat source for DHW and space heating. Due to the design of the home, which includes a connected green house, the low heat loss through the walls and the presence of a wood burner, a boiler will be used minimally. I am loathe to design a sophisticated system that includes a PID controller, injection pumps and the like when it is not expected to be used much. Not only the cost of the sophiscated system but the complexity of it bothers me when a simple mixing valve/dumb thermostat might suffice.

Any words of wisdom?

Brad White_88

Use the Force, Skywalker....

"I am loathe to design a sophisticated system that includes a PID controller, injection pumps and the like when it is not expected to be used much."

With the abundant solar, passive mass and retentive properties designed into what seems to be a remarkable structure (is there a such thing as envelope envy?) you may well need some PID control.

My round-about Socratic method here has me asking a spate of questions in no particular order (hence circular logic):

What is the capacity of the heating system you wish to control? IOW: How much are you counting on the passive, retentive and alternate heating means? How much is much?

If you answer that you have 100% of the heating needs then I have to ask if you are over-sizing.

If you answer that you are relying on the passive means to maintain the temperature most of the time but will install a 100% back-up heating system then that is the beast you must control.

If you answer that the back-up heating system is to maintain temperature across a week of cloudy cold days when the house is unattended/unoccupied, then the need for fine control is significantly diminished. But if that week is occupied, the need is further cemented. I speak of comfort, not energy here. Control for comfort, energy savings (or, better management of the free stuff,) will follow.

Another angle in all of this is that you are using active solar for heat as well... that has to be intelligently controlled or you may be reaching for the window cranks more often than you think. How is that being controlled? How integrated with the boiler? Why not have them share the joys of anticipitory control?

My biggest concern would be naturally overheating and the PID controls go a long way to keeping ahead of the curve (so to speak and as you well know). Further, if you let the heat loss get away from you and you have all of that mass, what is your time expectation to reach comfort?

In summary, I see the control sophistication parallel to the heating system's importance and role in this endeavor.

My $0.02-

Brad

Rich W

comlex

If you had a warm air system and a Trombe wall with dampers- that would be simple.

I agree with Brad. You've got too much going on there to get by with a "simple" control.

Good luck