Friday, March 9, 2012
In the winter, I love the crackle of the hot water moving through the massive cast iron radiators. The heat they radiate wraps me like a warm blanket. But a simple, old-fashioned gravity fed boiler system has a time delay from the trigger on the thermostat to the delivery of the heat. They also have one mode: ON, at a given water temperature. In a previous house, I researched all sorts of possible system improvements, including thermostats with larger setbacks and a boiler temperature regulator which would adjust based on outdoor temps. But even then, it would be hard for the system to overcome a 40 degree temperature swing in one day.
And then you get into the heating and cooling season. You know, heat in the morning and the cool at night. You can just open up the window, and let out all that hot air (which you just paid to heat…). But that isn’t possible in many commercial buildings, so on comes the A/C. It is at this point that you can forget about all of the efficiency ratings on the HVAC equipment - for you are constantly battling the effects of one with the other. My air source heat pump bills often shoot through the roof in the fall and spring, because it is basically a cooling compressor system, with an electric coil resistance heater. And in areas with high electric power costs, these are expensive to use. These in-between months also generate the largest number of complaints, which can turn into very real labor expenses for property maintenance personnel.
(ICF) walls. With the heat absorption of the concrete mass, these are also very effective in modulating temperature swings around the interior set-point. It would also get rid of those nasty drafts that makes you feel uncomfortable, even if the average temperature is o.k. Of course, this insulated house approach presumes that the windows stay shut in all but temperatures which are equal to your interior desired temp. But given the increase in allergies, having windows closed during high spring pollen counts is perhaps not altogether a bad thing.
What about HVAC solutions? Both air and water are good transfer mediums, as they can provide a gradation of temperature. But they need mechanisms to cool and heat the medium, either active or passive… So I go back to the #3 on my Top Wish List. This would combine a passive thermal system to collect and transfer heat to storage tanks with a small geothermal system to provide the cool water. Or the city water might come in cold enough. Then, mix the right temperature water, deliver via radiant cooling/ heating in ceiling panels.... or similar. You get the idea - simple, efficient, lowest tech for greatest passive survivability.
There are many innovative solutions, but the point is to recognize the reality of short cycle temperature swings. I'm not a HVAC designer, but would encourage considering not not just average daily temperature, but also the hourly the actual temperature highs and lows. Not just in the sizing of th equipment, but in it's ability to accommodate rapid temperature demands. These may be small enough to be resolved with the adding on and removing layers of personal insulation – ie sweaters. But the need is real, and one which I suspect is often overlooked both by HVAC equipment manufacturers and system designers.