Solar thermal water heating systems are highly efficient because evacuated tube solar collectors are designed to maximise the solar energy absorbed while minimising heat loss through radiation.
This system substantially reduces the amount of ‘parasitic’ energy lost (energy used up by the system itself during the process of converting solar energy to heat). As a result, it requires smaller pumps to circulate the fluid in the evacuated tube collector which means that there are fewer drops in pressure through the system, giving a sustained level of heat.
As a result solar thermal heating is the most realistic renewable energy solution for most commercial building applications.
However, solar systems require some form of storage and this is not necessarily the most efficient way to deliver hot water when the primary heat source is from a boiler.
Water storage can mean Legionalla problems and one answer is a hybrid water heating system employing solar thermal technology combined with a low water content plate heat exchanger which can provide hot water instantaneously, “topping up” the water temperature as appropriate without the need for storage, other than that required for the Solar input.
Plate heat exchangers are ideal for use in systems with rapidly changing heat outputs because they are low water content and can therefore respond to changing requirements quickly.
They come complete with primary pump(s), a fast-acting motorised control valve on the primary circuit and a purpose-built PID controller to sense secondary water temperature and control the motorised valve.
They can also be accommodated into most building management systems via volt-free contacts and offer the controlled delivery of hot water over a wide range of demand requirements.
This system ensures peak efficiency from the boiler because it involves heating the water instantaneously through the plate heat exchanger on a modulated control valve without feeding into any kind of storage.
The potential possibility of legionella breaking out into the system is greatly reduced since the water temperaturte is raised instantaneously by the plate to 60C, provided the plate is sized to deal with the full load instantaneously. The water will be at a high enough temperature to kill off any legionella.