AT-90-20-1 -- Analysis and Simulation of Outdoor Reset Control of Radiant Slab Heating Systems

A common approach to the control of radiant slab heating systems in residential and light commercial installations is outdoor reset control, where, given constant circulator flow rate, the temperature of the water sent to the slab (referenced to setpoint) is proportional to outdoor temperature (referenced to setpoint). In this paper the transfer function of such radiant heating systems is derived and discussed. Simulations are presented showing that this open-loop temperature modulation approach responds effectively to step disturbances in both indoor and outdoor temperature. The simulations show outdoor reset to be a less effective control strategy than flux modulation in response to daily sinusoidal variations in outdoor temperature.

KEYWORDS: radiant heating, slabs, floor heating, controls, water heating, heat flow, weather compensated controls.