An experimental facility consisting of two 3 x 4.4 x 3.8m (9.8 x 14.4 x 12.4 ft) rooms identical in construction was built. The test facility was designed to enable simultaneous comparison of two different control strategies, each implemented in a separate room. Each room was installed with a gas-fired boiler supplying hot water to the radiant floor heating system. An electrically heated storage tank was also installed in the circuit so that hot water to the floor slab could be supplied directly from the storage tank. This latter arrangement was found to be useful in accurately assessing the performance of different flow-modulating control strategies. Four different control strategies were evaluated. 1) Conventional air temperature-based on-off control. The pump is operated in on-off mode to maintain room air temperature within chosen limits. 2) Digital PI control. A PI controller is used to modulate the two-way valve to maintain room air temperature at the setpoint. 3) Floor slab temperature-based on-off control. The pump is operated in the on-off mode to maintain the slab temperature within high and low limits. 4) Two-parameter (air and floor slab temperature) on-off control. The pump is operated in the on-off mode to maintain both room air and slab temperatures within desired limits. Feedback signals from the room and slab temperatures were used in alternate sequence to control the pump. Results show that two-parameter on-off control keeps the room air temperature and slab temperature within reasonable limits and gives good temperature regulation. Being simple and cost-effective, it is a good candidate for radiant heat control.

KEYWORDS: year 1997, Temperature control, radiant heating, floor heating, experiment, testing, comparing, room temperature, slabs, gas fired boilers, hot water supply, accuracy, performance, controls