Hot Water in a Building

Domestic Hot Water (DHW) is the provision of hot water distributed at approximately 50oC to be used for hand washing and other personnel requirements. Provision of hot water is essential for many buildings through the need to provide toilet and kitchen facilities. It is important that this it is considered in the overall carbon performance of a building as any building with running hot water could incur surprising energy demand.

The type of hot water system installed will have a direct impact on the asset rating of the building. One of the main considerations is the fuel employed to store and provide hot water. For the production of an EPC a DHW system is applied to every zone, not just the zones containing the provision of hot water. This enables a demand profile to be utilised in the calculation based upon the number and types of zones.

Boiler (LTHW) 
Low temperature hot water boilers produce hot water at around 90 degrees centigrade and are the type most commonly found in domestic properties, the significant different between a domestic and commercial boiler is size, the latter being much larger. Hot water produced is distributed commonly via pipe work, thus the term 'wet' heating system.

Heat Recovery
This is the process of capturing heat that would normally be wasted. In the context of a heating system several methods are available to recover the temperature of the air removed from a space as part of the ventilation process and use it to pre-heat the supply air. This increases the efficiency of the system as the heat generator has a reduced demand.

Seasonal Efficiency
A measure of the percentage of heat from the combustion of gas and from associated electrical equipment which is transferred to the space being heated during a year under specified conditions. The seasonal efficiency will enable the calculation of useful heat output from power input, for example a boiler with a seasonal efficiency of 70% will need a power input of 143kW to produce 100kW of heating demand.