Domestic Hot Water

HVAC tab in model data


The effect of hot water consumption (hot water taps, showers etc) on building energy use can be included in your thermal model by switching on DHW on the HVAC tab.


Domestic Hot Water (DHW) is modelled in DesignBuilder by using hot water consumption rates based on the activity in each zone.  DHW hot water consumption is defined on the Activity tab and the definition of the hot water generating equipment is described below) is defined on the HVAC tab.


Three types of DHW are available:


1-Boiler - heat is supplied by the same boiler used for heating the building

2-Gas - gas-fired hot water system

3-Electric - electric immersion heater

Delivery hot water temperature

The temperature of the water supplied to the taps.

Mains supply temperature

The temperature of the water delivered to the building. This can be approximated to the annual average outside air temperature.


The operation schedules define the timing of the hot water draw off when the Timing HVAC + natural ventilation operates with occupancy option model option is not selected. The profile of hot water consumption in the EnergyPlus simulation is calculated from l/person/day data (gal/person/day in IP units) entered on the Activity tab by first estimating a typical number of hours per day. When typical workday schedules are used, this is simply the number of hours occupied during the working day.  When 7/12 schedules are used the typical occupancy hours per day is determined from January Monday data.


Note: When using a Compact schedule to define DHW operation DesignBuilder assumes a fixed 8 hours per day operation when calculating the maximum m3/s hot water draw off for passing to EnergyPlus.


DHW volumetric consumption supplied to EnergyPlus is calculated as:


DHW (m3/s) = DHW (l/day/m2) x 0.001 x m2 / (Typical hours per day x 3600)

DHW Type

A range of DHW types can be selected but note that different types of DHW system do not affect results in EnergyPlus simulations, apart from 1- Same as HVAC which causes heating CoP and fuel to be taken from the heating system. Other options all give the same results.


1- Same as HVAC
2- Dedicated DHW boiler
3- Stand alone water heater
4- Instantaneous DHW only
5- Instantaneous Combi
6- Direct (or off-peak) electricity
7- Heat pump