More than Heat

Faced with the choice between changing one's mind and proving that there is no need to do so, almost everyone gets busy on the proof. ~John Kenneth Galbraith

Comfort VS. Energy Savings. Not Necessarily a Juxtaposition!



PRINCIPLE THREE:
Design conditions rarely occur.

H ave you ever thought how little of the heating season is at design conditions? Table 1 from ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) reminds us how many hours each certain temperature occur. First, the basic math: 24 hours per day x 365 days = 8.760 hours per year. In New England, the outdoor temperature is above 72 degrees (cooling mode) approximately 700 hours. Simple subtraction tells us that we need heat in our homes for nearly 8,000 hours. If design conditions are usually no more than 100 hours, then for 99.9 percent of the heating season, the building can be heated with boiler or less water temperature.

PRINCIPLE FOUR:
Designing around the minor load is backwards.

T here is no question that Americans demand air conditioning. Their automobiles and offices are cooled and they want their homes to be places of refuge during the hottest summer days. But to design a heat delivery system around the cooling load is to let the tail “wag the dog”. So what are the options?

A stand alone cooling system is best, where the cooling ducts are near the ceiling and the heating registers or radiation are near the floor where they belong. Other products that should be offered to the consumer looking for the best comfort system are split type air conditioners and high velocity air conditioners. These should be part of any comfort contractor’s arsenal of choices. The problem is, if the homeowner calls a duct work guy, they get a “dry” ducted solution. If they call a plumber, they get a “wet” piped solution. The key player is the company that can integrate both wet and dry; ducted heating and cooling in the upstairs sleep zones powered by a fan coil off a hydronic heating boiler, radiant floor heating in the great rooms and vaulted spaces, and finally, multiple zone baseboard or radiators (convective or radiant) elsewhere. One indirect fired domestic hot water tank completes the system. Why have multiple burners and flues when one highly efficient, properly maintained power plant can do it all? It is the beat way, makes sense, and is cost effective. Remember, the heating equipment is the only thing that will pay for itself over time by investing in better efficiency or quality.

PRINCIPLE FIVE:
Temperature modulation is more Efficient.

I t has been consistently proven world wide that for every three degrees a building’s heating supply water or air temperature is reduced (and still heat the building comfortably), fuel consumption is reduced by about one percent. It is simple physics. For example, a packaged boiler that bounces off 210 degrees versus a system with modulated water temperature at an average of 150 degrees, would save approximately twenty percent on the fuel bill (210 degrees – 150 degrees = 60 ÷ 3 = 20) With our standard way of controlling heating systems (intermittent circulation), every time a thermostat calls for heat, the burner will fire until either the high limit is reached or the thermostat is satisfied. Since the thermostat doesn’t know how cold it is outside, it will “step on the gas” until it is satisfied. The thermostat will then be asked to “step on the brakes” against this freight train of hot water to keep from over-riding the setting on the thermostat. Heat anticipators were added to thermostats to combat this symptom of our design, not to fix the problem of overcycling with water that is almost always way too hot. And remember Principle One: heat always goes to cold; so all this super hot water piping will fight like crazy to cool off. Take a look at the heating curve in table 2 (below). The curve at 1.6 shows a typical water temperature curve that would be needed to heat the typical home that has copper fin baseboard. As you can see, at zero degrees outdoors temperature, the system should still get its 180 degree design water temperature, but at every other point of weather, the outdoor controller will lower the water temperature. Conversely, the zigzag curve shows a traditional cycling pattern on most boilers. It is easy to understand that the first example would be more efficient. Changing water temperature according to outside conditions should be done even if the system stays with the on/off circulation. Let the thermostat control the pumps and/or zone valves, but let an outdoor sensing control fire the burner.