Case Study # 1
Heat Recovery System
Recommendations
Comparison
The following table compares both heat exchangers mentioned in the previous results page:
Manufacturer/origin |
Ygnis (France) |
Bowman (UK) |
Characteristics |
4 tube passes, counter-flow |
Shell and tube, counter-flow |
Maximum admissible temperature |
280 ºC |
700 ºC |
Main application |
Exhaust gas from Boilers |
Exhaust gas from gas/diesel engines |
Energy recovered |
255 kWh/day |
300 kWh/day |
Estimated cost |
£ 1,200.00 |
£ 4,000.00 |
As it can be seen on the previous table, the Totaleco will not be able to
recover as much heat as the Bowman heat exchanger will. However, considering
that the Bowman heat exchanger is three times as expensive as Totaleco, and
that the energy recovered is just 45 kWh/day lower, Totaleco is going to be
considered in this study. For a small installation as the Dowhill farm, this
seems to be the best alternative.
Design of the closed loop integrated into the boiler room
Once the selection of the heat exchanger is done, its integration to the
existing installation has to be considered. In order to do so properly, a
brief estimation of the needs of the farm has been assessed. Based on the
capacity of the boiler in site, it was estimated that an average of 480 kWh/day
is needed for space heating and to produce hot water for the facilities. Considering
this value, the existing boiler cannot be substituted by the heat exchanger,
but its use can be reduced considering it as a back-up. Many configurations
are available to integrate the heat exchanger to the heating system; however,
the ones chosen for the project are those that combine it as an economiser
of the boiler (inlet temperature: 60°C/ outlet: 80°C).
The loop is integrated to the inlet of the boiler. In this way, the heating
water will be pre-heated in this loop before going to the boiler. Then, if
the temperature is high enough, the boiler does not need to be activated.
Consequently, the overall consumption of gas for space heating and hot water
production will decrease.
Loop including regulation integrated as an economiser
The heat exchanger is directly integrated to the heating system. A pump is provided circulate the water. An air cooling heat exchanger is foreseen to release excess heat in the system if the water temperature is higher than 80°C. The three way control valve will control this equipment.
Loop including regulation and storage integrated as an economiser
Considering that the heat exchanger cannot be bypassed and consequently sometimes
it will recover more heat than needed, storage can be integrated. It has been
sized to store the energy provided by the maximum energy recoverable minus
the minimum demand in the farm. The approximate size is 2 m³.
Cost Analysis
TOTALECO heat exchanger from Ygnis
Break-even: 2.1 years
Pay-back: 1.9 year
NPV after 10 years: £ 15,048.69
Heat exchanger from Bowman
Break-even: 3.3 years
Pay-back: 3.0 years
NPV after 10 years: £ 14,543.84
Conclusion
The Totaleco heat exchanger is then more suitable for the needs of the Farm.
Indeed, even if it is not the more efficient solution, its low price gives
it a big advantage and will make all the installation more profitable.
This will represent an economy of more than £ 200.00 per month.
» Go to Case Study #2: Glycerine Applications
