Building as a Dynamic Calorimeter: Determination of Heating System Efficiency: Fid-Bau Portal

Building as a Dynamic Calorimeter: Determination of Heating System Efficiency

K. Subbarao / J. Burch / H. Jeon

A building can be used as a dynamic calorimeter to determine an unknown, complex energy flow that is difficult or impossible to measure directly. Examples of such intractable processes include delivered energy from a heating, ventilating, and air conditioning (HVAC) system and solar gains. The basic idea is to first construct and calibrate a building model that allows inference of all major energy flows in the building (excluding the one unknown complex flux) from a few simple measurements. One then admits the unknown flow and relies on the whole building energy balance to determine the unknown heat flow. In this article, whole building calorimetry is used to determine the efficiency of a residential forced air gas heating system, before and after retrofitting the system. The building model must first be chosen as appropriate to relate heat flows to measured driving functions. Building parameters which are input to the model must then be determined. The data channels for obtaining the parameters for heating problems typically include a few temperatures, incident solar radiation, electric power into the building, and wind speed. It is necessary to use limited control of internal temperatures and electricity gains during the short term tests to minimize errors in parameter extraction. In other words, it is essential to follow a carefully specified test protocol. After this calibration, the heating system to the house was turned on and observed for several days. Heating system efficiency is obtained by integrating the heat flows over some interval and dividing by the measured total gas input. This efficiency is the net result of combustion losses as well as distribution system losses to the unconditioned basement. For the furnace tested, initial efficiency was 52 +- 2%. After the system was retrofitted (mainly increasing the fan flow rate and taping some duct leaks), the efficiency increased to 58 +- 2%. (ERA citation 11:054089)