Heat Recovery Systems – what are they and how do they work?
In simple terms, heat recovery systems work by drawing on the potentially valuable warm air or water in a factory, and getting it to work just a little bit harder.
The heat exchanger is the brain of the heat recovery system, moving the stale air through hundreds of small pipes whilst drawing in cold air from outside in other ducts. These flow past each other without mixing physically but the heat is drawn from the stale air to the cold air, which is then fed back down into the pipes and into the plant. The stale air, minus its heat, is then expelled into the atmosphere.
Types of Heat Recovery Systems
Heat recovery systems can come in a variety of forms, but all involve some form of heat exchanger. We detail these different forms below:
- Heat Recovery Wheels
The wheels can be oriented side-by-side or on-top of each other and the exchanger can be mounted vertically or horizontally directly on-site. The wheels rotate in opposite directions to each other and the energy from the stale/exhaust air is transferred to the incoming air, heating it up. The heat exchanger wheels are normally made of aluminium, but can actually be constructed from a wide range of materials including plastic and even paper. The benefit of the thermal wheel is that it is highly efficient (up to a maximum of 80%) compared to other systems and is likely to provide a quicker return on investment.
- Plate Heat Exchangers
Plate heat exchangers are essentially a box with a series of parallel plates made from metal or plastic which allows the extracted air to pass over the incoming air, transferring the energy and heating it up. The air streams are separated by the plates and never touch, so one of the key factors in the efficiency of any system is how thin and conductive the individual plates are. Many of the most efficient systems are made from aluminium, with the high standard alloy of the plate assuring the high durability of the products.
- Run Around Heat Recovery System
A run around coil can be introduced to an existing air handling system and typically consists of two coils that are connected to each other by a pumped circuit of pipes. Water is normally used to charge the circuit, picking up the heat from the exhaust pipe and transferring it to the supply air coil. Heat recovery systems such as these are used where the two air streams are not close enough for more efficient systems, such as the thermal wheel or recuperator technology. For example when airflows are required to be completely separate (e.g. hospitals). It generally delivers a maximum efficiency of around 50%.
- Heat Pumps
Heat pumps take the heat from one area and transfer it to another location. They operate in a similar way to a refrigeration unit and can be used for both cooling and warming the air. There are a number of different varieties and they can draw heat from the outside air, as well as from the ground through the use of a network of pipes.
The Benefits of Heat Recovery Systems
Now we take a quick look at the benefits of these Heat Recovery Systems:
- With heat recovery ventilation systems you can supply a much cleaner and more constant air environment for employees at any time in the year, keeping them cool in the summer and warm in the winter with smart technology.
- Installing something like a flue economiser onto a large boiler can increase its lifetime because it is not subject to sudden high temperatures that cause excessive wear and tear.
- Greater reductions in heating costs because you are using boilers and ventilation systems more efficiently.
- Significantly reduce the levels of carbon dioxide emitted.
- For businesses there is also the credibility that comes with working in a greener environment.