An experimental study of multiple parameter switching control for radiant floor heating systems

An experimental facility consisting of two identical 3 X 4.4 X 3.8 m(3) rooms has been built. Each room has a gas-fired boiler supplying hot water to the radiant-floor heating system. An electrically heated storage tank installed in the circuit ensures that hot water to the floor slab is supplied directly from the storage tank. The facility serves for instantaneous comparisons of two different control strategies implemented in separate rooms. Two flow-control schemes were tested and evaluated. We used (i) a conventional on-off control for a valve controlled by feedback from the room thermostat and (ii) a two-parameter switching control (TPSC) with switching intervals ranging from 30 s to 60 min. With this strategy and a switching time of 10 min, the valve is operated in the on-off mode for the first 10 min based on feedback signals received from the slab-temperature sensor and during the next 10 min, air-temperature signals from the thermostat control the valve. This latter strategy is shown to be better for radiant heat control under continuous and intermittent modes of operation than to conventional on-off control. (C) 1999 Elsevier Science Ltd. All rights reserved.