Kennedy Controls specializes in innovative solutions to complex business problems.

The Kennedy Controls Corporation specializes in innovative solutions to complex business problems.

Problem - What should the temperature be?

The energy consumed for heating and cooling, and therefore the cost of heating and cooling, is proportional to the difference between inside and outside temperatures. When the inside of the building and the outside of the building are the same temperature, no energy flows in or out of the building. The greater the difference between the building’s inside and outside temperatures, the more energy flows. Heat energy flowing out of the building in the heating season and heat energy flowing into the building during the cooling season require purchased energy to offset the flow so the desired building interior temperatures can be maintained.

If a building's temperature could be allowed to be as close as possible to the outside temperatures during times of the building’s non-use, (nights, weekends, holidays, vacation periods, etc.), the heat transfer would be minimized. If the heat transfer were minimized, the energy cost would be minimized as well. The difficulty in a management scheme to achieve the above goal is complicated by a number of factors. Consider heating a school building in the winter, for example. If a given class room has a thermostat, its function is to maintain the same temperature in the classroom all the time. Therefore heat loss during the non-use period of the room is much greater than it would be if the temperature in the room were allowed to lower somewhat.

The simplest attempt at a solution would be the use of a timed thermostat or other timing device connected to the thermostat. For instance, one could lower the classrooms desired temperature from 72 to 62 for the period of 5 PM to 6AM. Definite savings would result, but there are four complications. First, the selection of 62 degrees for the non-use period desired temperature was arbitrary. Could it have been 52, for instance? More savings would have resulted. Could it have been allowed to leave the temperature ‘down’ for a longer period. . . say until 7AM, for instance?

Second, what about weekends or school holidays? And perhaps more important, what about returning the temperature back to normal for special events or meetings held at night or weekends.

Third, since the outdoor temperature is always changing, doesn’t all of the above have to change to match the outdoor conditions – in other words, if it isn’t so cold (or windy) out on a given night could the setback period be longer than if it was colder? Of course, the answer to that one is yes – but how much longer could it have been?

Fourth, if the setback was for a longer period it could be ‘deeper’. For instance, consider the difference between an overnight setback and a weekend or holiday setback. If an overnight setback is too deep, the system may not be able to restore the room to the desired temperature on time. On the other hand, a deep setback can be used when the setback period is for several days, as the setback wouldn’t be ‘undone’ by the requirement of an early return that took a large percentage of the setback time.

All of the above is for one room. The thermal characteristics of a given room are unique to that room. Every other room in that building has a different set of characteristics based on its makeup, its location with respect to other rooms, the direction it faces, capability of the heating system in it, and a host of other factors.

As you can see, the optimization of any set back program is based on a number of conditions as explained above. . . but the most significant conditions are ones that have to do with the variability of the weather, or the ‘weather pressure’ on the building. Weather pressure as used here is a term used to identify a plurality of characteristics. The most obvious is the temperature outside. Another factor is the wind outside. Higher wind causes more effect on the building through both degradation of the stationary or boundary layer of air on the outside of the building and by increasing infiltration loss through increased leakage around doors, windows, ventilator openings, etc. A third factor is the effect of the sun on the building. There are other factors that play a role in weather pressure as well. The sophisticated data gathering and proprietary algorithms the computer executes in the KenTrol software plus the individual room KenTrol WatchDogs are required to resolve the complex mathematical problems and operate the system for maximum energy savings.