The owners report that, although the system is generally comfortable, they’ve noticed the main living room areas served by the panel radiators get cool and remain that way for two or three hours whenever they turn up the basement thermostat. Other issues reported by the owners include having to replace some burned-out heating elements in the boiler, air noise in the system, occasional flow noise when only one panel radiator is operating and heat migrating into the floor heating portion of the system when the panel radiators are operating.
There are several issues with this system. They include:
• Electric boilers require a minimum flow rate whenever they operate to prevent their elements from overheating. If only one panel radiator is operating, it’s likely that this minimum flow rate through the boiler would not be met, and hence the underlying reason for the burned-out elements.
• The use of a fixed-speed pump, in combination with the thermostatic valves on the radiators, requires some means of differential pressure control. Without this control, flow noise can occur at the thermostatic radiator valves when only one of the radiators is allowing flow, and thus, the fixed-speed circulator is operating at high differential pressure.
• This design places the panel radiator subsystem and the floor heating subsystem in parallel. Without check valveson the return side of both subsystems, flow reversal is possible whenever one subsystem is on and the other is off. This is likely the underlying reason for heat migration into an inactive subsystem when the other subsystem is operating.
• The drop in heat output from the radiators when the basement floor-heating thermostat is turned up is due to the high-thermal mass floor slab temporarily absorbing heat at a rate higher than the output of the boiler. This transient condition would eventually diminish but would reoccur each time the thermostat controlling the floor slab portion of the system is turned up, especially following a deep setback condition.
• The noise coming from two of the thermostatic radiator valves is due to a reversal of the supply and return piping connecting at the bottom of the radiator. This reversal causes flow to move backward through the radiator’s valve, which can result in cavitation or “thumping” sounds when the valve plug is close to its seat. Most panel radiators have specific requirements on where the supply and return piping connect. The most common configuration has the supply on the left, and the return on the right, as viewed from the front of the radiator. Technicians should always verify that flow passes through radiator valves in the correct direction. Small details matter...