Types of Techniques
There are various techniques for Heat Recovery applicable to various processes and systems. But fundamentally it must be said almost all such techniques utilize either;
- Heat exchangers
- Energy(enthalpy) recovery wheels
- Direct application for beneficial use
- Use in a secondary stage of a process
Heat Recovery with Heat exchangers
A heat exchanger is used to transfer thermal energy from one fluid (liquid or gas) to another. The waste heat in the fluid is recovered through conduction (physical contact via the conveying tubes).Some examples are the engine cooling systems (radiators), oil coolers, Space heating Radiators, Water cooled condensers (air-conditioning), Air to air heat recovery (flue vents), condensing boilers etc. Combined Heat Generators (CHPs) are made highly efficient due to the use of heat exchangers to recover the waste heat.
Energy (enthalpy) recovery wheels
The Energy /Enthalpy recovery ventilators utilize desiccant rotors to adsorb and regulate moisture in the fresh air or exhaust air (depending on whether the application is cooling or heating) while recovering the cooling or heating effect. In colder seasons you require moisture and heat in the space while in the hot seasons you have to get rid of it for your room comfort. An efficient domestic ventilation system which maintains good Indoor Air Quality ( IAQ ) either recovers moisture when it is most needed ( in winter) while expel while retaining the low temperature when it is least needed (in summer) all the while maintaining a fresh air supply. The recovered energy can be as high as 40 to 75% of that otherwise would have been expelled.
A good example would be the car heating systems where engine heat is utilized to warm the car interior.
Use in a secondary Stage of a process
There are many processes in which the primary stage liberates much energy which go a waste. A secondary stage uses this heat recovery to boost the process to a higher efficiency. This makes the residual matter also less.
A good example is the high efficiency pellet or wood chip boiler.
Make no mistake! Recovered energy is as good as saved money .By limiting the consumption of fuel heat recovery provides solutions to many global problems such as fuel shortages, green house gas emissions, recession and many others.