BOILER ENERGY BALANCE
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.
