Heat Recovery

Heat recovery can be achieved in a number of ways subject to applications. Some typical examples are:

• Recuperators operate in a similar way to plate heat exchangers, by passing the air being extracted from a building across one side of the plate and the incoming air over the other side of the plate, the temperature difference during cold outside conditions will allow a transfer of heat into the cold incoming air. A series of these types of plates assembled together will form a recuperator and is commonly used in all types of ventilation systems.
  
• Run-around Coils are often used in air handling units (AHU’s). A fluid, generally a glycol mixture is circulated via a pump set, through a coil situated in the exhaust air path of the AHU. This picks up the latent heat that would otherwise be thrown out to atmosphere. The heat is then transferred into the working fluid and given up into the cooler supply air path of the AHU via another coil.

There are many situations where in the region of 55% to 60% of wasted heat can be recovered.

Optimisation

Conventional time control requires a warm up period to be allowed at the commencement of each heating period. The warm up period would normally be set to make allowance for the worst winter conditions. This means that during milder weather the system would start much earlier than necessary and therefore waste energy. The optimum start monitors the actual warm up period and also the degradation of temperature after the system has switched off.

By building up this data the optimum start can calculate the actual period required to bring the area up to the required temperature by the time required. This method is accepted to make a saving of approximately 50% of the traditional warm up period i.e. if a system without optimum start would normally have a one hour warm up period allowed then the average saving over the heating season would be 0.5 hours per day. An 8 hour day plus the normal one hour warm up would be 9 hours. A saving of an average of 0.5 hours per day would therefore represent in the region of 5.5% fuel saving over a heating season compared to a conventional time and temperature control system.

Zone Control

Zone control is essential where a building is divided into a number of areas each with independent time and temperature requirements. A well designed zone control system would have boiler interlock so that when all zones are either up to temperature or outside their timed on period the boiler plant would switch off until there is a demand on one of the zones. Each zone can also have independent optimum start as described above.

The combination of these items in a well designed zone control system will have a significant reduction in running costs as well as minimising carbon emissions to atmosphere.

When installing a zone control system onto an existing heating installation it is essential that it is designed with a full knowledge of the various types of system to ensure that the zone valves are installed in the correct position and any additional modifications to pipework are carried out to allow the valves to provide the required function.