Copyright Goodheart-Willcox Co., Inc. Chapter 12 Radiant Heating Systems 261 When sizing the circulating pump for the entire system, add the total flow of all loops combined. However, when calculating the feet of head for pump sizing, simply select the loop with the highest pressure drop. Remember to add the sup- ply and return piping between manifold stations and any other devices that the circulator will be serving when calculating feet of head. 12.7 Radiant Heating Controls Controls for radiant floor heating systems can be simple or complex, depending on the size and application of the system and the desires of the heating designer for increased efficiency and performance. Some components for controlling a radiant floor heating system include: ■ ■■ Space thermostats ■■ Electric or electronic zone valves ■■ Flowmeters ■■ Temperature gauges ■■ Floor or slab sensors ■■ Outdoor reset controllers ■ Microprocessor controllers Space thermostats: Today’s space thermostats used for radiant heating con- trol provide many features not found on conventional thermostats, including touchscreen design, seven-day programmable scheduling, and auxiliary sensor inputs for monitoring floor temperature and outdoor air temperature. In addi- tion, space thermostats can directly control zone valves or be connected to a microprocessor panel for more precise temperature control, Figure 12-42. Electric or electronic zone valves: Low-voltage electric zone valves operate on a 24 V circuit and have been used widely in the hydronic heating industry for years. These are normally two-position zone valves designed to operate directly from a thermostat or through a relay control board, Figure 12-43. Electronic zone valves are microprocessor-driven valves that offer better temperature control through modulation, Figure 12-44. These valves can open and close anywhere between 0% and 100% of their total range to provide optimal control based on space heating demand. In addition, electronic zone valves do not rap- idly spring-return closed, which lessens the chance for water hammer within the circuit. Photo courtesy of Watts Figure 12-42. An example of a modern thermostat used with radiant heating applications. Goodheart-Willcox Publisher Figure 12-43. This is an example of a two-position zone valve that can be controlled directly from a thermostat or control panel. Goodheart-Willcox Publisher Figure 12-44. This is an example of an electronic zone valve that has modulating capability.