Unvented Domestic Hot Water Cylinders
Use a pressurised water supplied from a storage cistern tank pumped via ‘ booster pump’ into the cylinder, the advantages of these systems are the higher pressures obtainable at sinks also with very good flow charactoristics coupled with a balanced cold supply makes these systems particularly attractive for showers. Extremely low heat loss from these cylinder and fast recovery (reheat-up) time makes the unvented cylinder a must in any solar thermal energy efficient upgrade and new build projects.
The disadvantages of these system are sometimes overlooked, in hard water areas, the build up of limescale around the safety features such as the T + P valve could make those valve ineffective. Annual servicing of the system is therefore essential.
Unvented cylinders come with many safety features to insure that at no time the water temperature reaches 100*c as set down by regulations, a thermostat with a set point of 60*c , high limiting thermostat with a lock out of 90*c and a (T+P) temperature and pressure release valve with a designed release temperature of 95*c. Also the cylinders are supplied with a sealed expansion vessel which must be service annually to ensure working order as these will loose the trapped air rendering the vessel ineffective, resulting in excess pressure generated throughout the system.