Dienstag, 25. Juni 2013

Improving Diagnostics and Energy Analysis for Multifamily Buildings: A Case Study

One possible retrofit in buildings with old single-pipe steam heating systems is replacement of the existing brick-set steam boiler. These boilers are usually significantly oversized, have large standby losses, and thus have low seasonal heating efficiencies. Because of the difficulties associated with separating envelope and distribution system performance from boiler performance, energy bill analysis is not adequate for evaluating boiler replacement as an option. However, boiler surface-temperature measurements, heat-flux measurements, and stack heat-loss measurements can be used to make a detailed energy balance the boiler. Such a detailed energy balance contains the information required to evaluate both boiler retrofits and complete boiler replacement. We used the measurements made during our week-long experiment to make a detailed energy balance on the boiler. The surface temperature measurements, along with the boiler room air temperature were used to calculate the convective and radiative heat losses from the surface of the boiler during both on- and off-cycle periods. The heat losses from the steam pipes in the boiler room were estimated from short-term measurements of their surface temperatures. We used the temperature measured on the ground underneath the boiler, along with estimates of outdoor air temperature and the groundwater temperature to determine the conductive heat losses from the bottom of the boiler. The off-cycle stack heat losses were determined from the tracer gas measurements used in the vent damper tests, and the on-cycle losses were determined from steady-state efficiency measurements made by the MEO staff. The heat losses from the boiler surfaces were determined using simplified models of radiative and convective heat transfer, and assuming that the wall surface temperatures were equal to the boilerroom air temperature.