How to calculate the DHW demand of a home
What is the way to estimate the daily demand for DHW (in Spain) if the precise figure is not available? This data is essential in the evaluation of the energy efficiency of properties intended for housing and, although to a lesser extent, for buildings for tertiary use. The new Energy Efficiency report establishes the methodology for calculating the ACS reference demand in its Appendix F.
It is necessary to know the daily demand for DHW to make an energy certificate
The current edition of CE3X for the realization of energy efficiency certificates requests the incorporation of the value of daily consumption of DHW (liters per day) in the General Information section. This represents a change with respect to previous versions, where this information was only necessary for buildings for tertiary use, both small and large.
Calculation of daily DHW demand
The DHW demand It is regulated in the Technical Code: CTE-DB-HE4
Annex F of the regulations describes the procedure for determining the ACS reference demand. This appendix provides the tools necessary to calculate the total domestic hot water requirement. Once the demand is calculated, we can use that value as an estimate for consumption in CE3X if we do not have precise data.
ACS demand for homes
The ACS reference demand for buildings for private residential use it will be obtained considering
needs of 28 liters/day·person (at 60ºC), an occupancy at least equal to the minimum
established in table a-Annex F and, in the case of multifamily housing, a centralization factor
according to table b-Annex F, increased according to the thermal losses due to distribution,
accumulation and recirculation.
Demand for ACS buildings for use other than residential
In the calculation of the reference demand for DHW for buildings with purposes other than residential, the indicative values in table c of Appendix F can be used. These values represent estimates of the demand for DHW for uses not related to private housing, a a reference temperature of 60ºC. However, these values must be adjusted according to heat losses through distribution, storage and recirculation. In cases where the ACS reference demand is not contemplated in table c of Appendix F, it will be necessary to determine it from ACS needs verified by practical experience or sources of recognized credibility.