Metering system - usual point of measurement for Domestic Hot Water
We propose here below some guideline to define the points of measurement according to the energy use and the required breakdown of the measurement (the breakdown means how the energy use consumption will be reported, it can be reported as building global consumption or consumption per floor or area)
We need to consider :
- DHW production : primary energy that is necessary to heat the water
- DHW load : thermal energy delivered to the distribution system – it represents the need for DHW
These 2 values are linked by the following equation :
DHW production = heating system efficiency x DHW load
The heating system efficiency takes into account the boiler efficiency and the losses in the hot water storage tank.
Independent electrical boiler
Data to collect according to consumption breakdown :
- Global consumptions: aggregations of electrical boiler consumptions of each area
- Area consumptions: consumption of the boiler feeder
Method of measurement
- Direct metering :electrical meter
Remark : Hours counter is not possible as most of the boiler integrate their own control
Usual point of measurement locations:
- Feeders in the sub-electrical switchboards
Independent central gas boiler
Data to collect according to consumption breakdown :
- Global consumptions: gas boiler consumption and pumps consumption
- Area consumptions: difference of the supply and return flow of the dedicated area
Remark : Recirculation may or may not be present in the system
Method of measurement
Boiler consumption :
- Direct metering :gas meter
- Indirect metering :
- Solution 1: heat meter at the primary circuit– boiler efficiency has then to be taken into account to calculate the primary energy.
- Solution 2: in existing building, it is usual that hot water temperature (shall be above 50°C to avoid legionella problems ), cold water temperature and cold water flow are already metered downstream the hot water tank. It is then possible to calculate the DHW load with the following formula.
The heating system efficiency has then to be estimated in order to calculate the primary energy used for hot water heating.
Pumps consumptions :
- Direct metering :electrical meter
Area consumption :
- Direct metering :use of a flow meter at the pipe derivation
- Indirect metering : measure the hot pipe temperature of the corresponding area. Each time a run-off is observed, the temperature rise in the pipe of the area that consumes. The corresponding water consumption and energy consumption metered at global level can then be allocated to the area.
This method is only valid if the consumption of each area is separated in time, for instance this is not possible for a hotel.
Point of measurement locations :
- Boiler consumption : Boiler room
- Area consumptions : after the pipe derivation, but location may strongly depends on the water distribution
Combine with space heating
Only indirect metering allows then to split space heating from DHW production. The solutions described in the previous paragraph can then be used but heat meter shall be installed on the DHW distribution pipe system.
Solar heating
Some labels or standards require measuring separately renewable production, to be able to split the DHW produced by solar heating from those produced by heating booster, the following points of measurement shall be considered.
With electrical booster
With boiler booster
