Energy efficient ventilation systems | Archive Titles

TABLE 1 – Comparison of Heat Recovery Systems
Criteria	System type
	Thermal wheel	Plate heat exchanger	Run-around coil
Efficiency	44	4	–
Pressure drop	4	4	–
Power savings	4	44	4
Air leakage	–	4	44
Space available	4	–	44
Control	4	4	4
Transfer of odours	–	4	44
Frosting problems	44	4	4
Moisture transfer	44	–	–
Cooling energy recovery	44	4	4
Resistance to aggressive environments	4	4	44
Reliability	4	4	4
4 Denotes acceptable 44 Denotes very good

Table 2 – Relative benefits of incorporating higher efficiency elements into air handling unit specification
Type	5 m³/s air handling unit			8·5 m³/s air handling unit
	% increase in capital cost	% reduction in running cost	Typical payback period (years)	% increase in capital cost	% reduction in running cost	Typical payback period (years)
Standard ahu without heat recovery	£13 000	Base option	–	£17 000	Base option	–
Heat recovery options:
Extra over for thermal wheel	48·0	13·0	7·0	49·0	13·0	5·0
Extra over for plate heat exchanger	52·0	12·0	8·0	48·0	12·0	6·0
Extra over for run-around coil	35·0	10·0	7·0	40·0	10·0	6·0
Extra over for higher efficiency aerofoil fans	3·0	8·0	4·0	3·0	15·0	2·0
Extra over for higher efficiency motors	0·5	1·5	3·0	0·5	2·2	2·0
Extra over for variable speed drives	7·0	33·0	3·0	6·0	34·0	2·0

Table 3 – Effect of decreasing system resistance
Type	5 m3/s air handling unit		8·5 m3/s air handling unit
	% decrease in capital cost	% reduction in running cost	% decrease in capital cost	% reduction in running cost
20% decrease in system resistance	5·0	11·0	5·0	8·0
40% decrease in system resistance	5·0	22·0	5·0	15·0