Sharp JX-9400 Informações Técnicas descarregar pdf (Página 117)

in the three small units, and external recirculation above 20 per cent is

measured in three large units. These leakages signiﬁcantly aﬀect heat recovery

eﬃciencies, which drop from nominal values of between 50 and 90 per cent

down to actual values ranging between 5 and 69 per cent. On average, the

nominal heat recovery eﬀectiveness "

is 70 per cent, but the global, real

eﬃciency is only 43 per cent. In the best case, 80 per cent heat recovery

eﬀectiveness is reduced by 15 per cent down to a 69 per cent real eﬃciency.

Only 8 units out of 13 have a net energy saving larger than 1 Wh/m, as

shown in Figure 5.11. Note that 1 Wh allows heating one cubic metre of air

by about 38C. Negative speciﬁc net energy savings are observed in three

units, where the heat recovery uses more energy than it saves! The coeﬃcient

of performance of good units can be much larger than those of a heat pump

used for heating buildings, but is rather small in three units. A COP of less

than 2.5 indicates that the heat recovery is less eﬃcient than heating the air

with a gas boiler with 75 per cent eﬃciency (Ruyssevelt, 1987).

20%

40%

60%

80%

100%

0% 20% 40% 60% 80% 100%

Global recovery efficiency

Heat exchanger efficiency

Large units

Small units

Figure 5.10 Global heat recovery eﬃciency versus nominal heat exchanger

eﬀectiveness measured in several units

–1 0 1 2 3

COP

SNES [Wh/m

]

Large units

Small units

Good

Poor

Unacceptable

Figure 5.11 Seasonal average coeﬃcient of performance and speciﬁc net

energy saving of the tested units

96 Ventilation and Airﬂow in Buildings

1 2 ... 112 113 114 115 116 117 118 119 120 121 122 ... 210 211

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