A solar heating system can be constructed using the solar loop which comprises a combination of solar collectors, pumps, water tanks and water heaters. Solar collectors are connected on the demand side of the plant loop. Multiple collector modules can be combined in series and parallel. The supply side of the solar plant loop contains a water heater, circulation pump and setpoint manager to control the loop setpoint. A solar loop can be connected directly to domestic hot water (DHW) loop outlets by first deleting the water heater from the supply side of the DHW plant loop and then connecting the solar water heater to the DHW supply side splitter and mixer:
In order to realise energy savings with a solar heating system, it is best to use a two-tank system with a storage tank and an auxiliary water heater. The storage tank gathers heat directly from the solar collectors and stores it for later use. The auxiliary water heater is positioned downstream of the storage tank on the supply side of the DHW plant loop. The auxiliary water heater, or booster water heater, provides additional heat if the storage tank water is not hot enough. The auxiliary water heater can be modelled as an instantaneous/tankless water heater or as a standard tanked water heater with heating source (see Water Heater component):
Another strategy to consider for solar heating systems is to allow the storage tank to reach a much higher temperature than necessary for the end use. This allows the tank to store more energy from the solar collectors, when it is available. However, for applications such as domestic hot water, it is undesirable and unsafe to supply excessive hot water temperatures at the point of demand. To take advantage of higher storage temperatures, yet still avoid scalding temperatures at the tap, the hot water leaving the storage tank can be tempered with cold water using a three-way valve (tempering valve) to achieve the target temperature. An additional auxiliary DHW heating loop is provided by DesignBuilder HVAC which incorporates this arrangement. A solar loop water heater can be directly connected to the supply side splitter and mixer of an auxiliary heating loop:
Another common solar hot water loop arrangement similar to above but this time with auxiliary heating from a hot water loop with boiler:
This arrangement of components and loops models a typical solar heating system with 2 tanks: a solar tank with water at potentially high temperatures and an auxiliary tank containing water at temperatures that can be used by heating and/or DHW purposes. The Solar Assisted DHW HVAC template provides this functionality.
More information on how to configure and control Solar and Auxiliary heating loops can be found on the Solar Hot Water help page.
Why is the solar collector on the demand side of the loop?
The demand is the loop demand rather than a component demand, i.e. the demand is created by the need to satisfy the setpoint on the solar loop supply sub-loop outlet. In other words, the more the outlet temperature from the water heater element drops below the setpoint, the higher the demand on the collectors.