|What is trigeneration?
Hardly had the
public got used to the expression cogeneration and had designers begun plans
for equipping boiler rooms with cogeneration units, than a new expression,
which is far from being a household word, began to appear - tri-generation.
Translated, it means the combined production of electricity, heat and cooling;
technologically it is about connecting cogeneration units with an absorptive
advantageous from the operational point of view of cogeneration units, because
it allows the use of heat even in summer outside the heating season, and in
this way prolongs the annual running time of the unit. It is just this lowered
possibility of using heat from cogeneration units in the summer which leads to
the use of smaller units than would otherwise be suitable. If we are then able
to change heat into cooling, nothing stands in the way of cogeneration units
working to the full even through summer. The produced cooling can be used
everywhere where air-conditioning is needed - in banks, hotels, business and
administration centers, hospitals, sports halls etc. Air-conditioning equipment
can be of two types:
- compressor - an electric motor runs the compressor
- absorptive - run on steam, gas, heat from hot water
The advantage of
absorptive cooling (apart from the above mentioned possible connection with the
cogeneration unit) compared with compressor cooling is that it needs lower
quality and even cheaper input heating energy than the more expensive input
electric energy for compressor cooling. Absorptive cooling is also quiet,
simple and reliable. The disadvantages are mainly the higher investment costs
compared with compressor cooling, and bigger dimensions and weight.
The basic principal of the absorptive circuit is the replacement of compression by
heat procession in which the cooler absorbs a suitable material (absorbant) at
low pressure, then transfers to another exchanger working at higher pressure
where the cooler by the input of heat into the liquid is released (expelled)
again. The result is a cooler with higher pressure which resembles
condensation. What happens in the condenser and evaporator is similar to a
|How does a trigeneration works?
Absorptive cooling has three circuits among which a
change of heat occurs. The first is the heating water circuit which is the
drive medium for internal heat exchange. This circuit was connected to the heat
source, in our case a cogeneration unit. The second circuit is a cold water
circuit which is directly connected to the cooling circuit - similarly as in
central heating, but cold water flows instead of hot water, and which cools the
air in rooms - and in it removes heat from the area. The third circuit is the
cooling water circuit which removes water with heat for cooling. Cooling most
often takes place with the help of cooling towers.
The deciding influence on the size and price of cooling equipment is held by the
temperature of the hot water circuit. It is generally true that the higher the
temperature of the hot water, the smaller and cheaper is the cooling equipment.
Most industrially produced equipment works with a temperature of around 90 to
135°C. The cold water circuit works with temperatures necessary for the removal
of heat from rooms, and this is around 7 to 15°C. The cooling water circuit
which takes heat away from cooling equipment has temperatures of 20 to 45°C.
Tedom building with cooling tower
|Trigeneration in TEDOM
In order for test for ourselves the concrete possibilities of
tri-generation we decided to air-condition the office area of the Tedom
administration building. We installed a York International WFC 10 absorptive
unit for cooling, and this was built to use hot water with a low temperature,
e.g. connected to a cogeneration unit. A Premi 22 cogeneration unit with a max.
heat output of 45.5 kW works in this case with a heat drop of 95/75°C;
individual heating / cooling circuits have these parameters: hot water 95°C, cold
water 8°C, cooling (tower) water 24°C. This equipment has been working in our
firm since 1998 and proves that tri-generation can be used with low output