Heat metering

At a basic level a controller may offer the ability to provide an estimate of the heat in kWh supplied by the solar collectors to the cylinder by multiplying the difference in temperature between the collector and return from the cylinder by the approximate flowrate (taken from the pump speed, set-up at commissioning). The estimation in flow rates will result in estimates of heat gains that are probably about +/- 20%. A better estimate will be achieved if the controller can take an additional digital input from a flow meter inserted in the solar loop.

Data Logging

Several controllers offer either a self-contained ability to record the system variables over time or can link to an accessory datalogger or even to a BMS Building Management System. Although generally deemed an unnecessary additional expense in a domestic system, it may become essential if ROC payments for renewable thermal generation become available. On top of this, it is a valuable check that the system is working with something approaching its design performance. Since solar systems always operate with an auxiliary back-up that may be set to automatically compensate for solar shortcomings, then it can be difficult to determine actual solar performance, particularly given the variability of solar irradiance.

If heat-metering becomes established for the payment of Thermal ROCs in the UK, then probably only a meter from a recognised list will be permissible to verify the number of units generated. This is no doubt make its way to Ireland.