The key to our low energy use for water heating is a water to water heat exchanger which removes the need to heat the water in the cylinder to 60C, as standing water is never consumed.
The key aspects of this design are:
- Large capacity heat store and heat exchanger
A large capacity heat store can:
- Minimise relative heat loss due to small surface area to volume ratio
- Maximise heat exchange by allowing for a longer copper coil with a larger surface area
- Provide opportunity for demand-side management as the thermal store can be heated during low-cost periods and will retain the heat energy for long periods before topping up is required
Monitoring of energy consumption for water heating in one of the HHP houses over a 12-month period, where the heat source, an immersion heater, was left permanently on, showed that for occupancy of 2 adults the average daily energy requirement for hot water was 1,387 kWh/yr. For timed heating periods the total consumption reduces to approx 1100kWh for a family occupancy; this compares to a SAP (2005) prediction of 3,204kWh/yr, for an assumed occupancy level of 3.5.