Civil Engineering Reference
In-Depth Information
With:
e
Effectiveness of HRU (-)
Total ventilation heat loss (Jh/m
3
)
q
V
HDD
Number of HDD (Kday)
Increase in SFP (J/m
3
)
DSFP
f
g
Conversion factor condensing gas boiler (-)
f
e
Primary energy factor electricity (-)
Evidently, heat recovery operation will only be net positive for the total per-
formance of the ventilation system under the framework considered if the real
effectiveness is higher than the minimal effectiveness thus calculated.
To assess the performance of EAHP-based domestic hot water production as a
ventilation heat recovery measure, compared to air-to-air heat exchanger technol-
ogy, a similar definition of equivalent heat recovery effectiveness e
eq
is proposed. e
eq
is defined as the ratio of the energy savings achieved by the EAHP system in com-
parison with a reference system, converted to heat, and the ventilation heat losses:
=
f
g
Q
vent
e
eq
¼
f
g
Q
DHW
f
e
SPF
Q
DHW
ð
4
Þ
With:
Q
DHW
Annual energy for domestic hot water (J)
Q
vent
Annual ventilation heat loss (J)
SPF
Seasonal performance factor EAHP (Kday)
f
g
Conversion factor condensing gas boiler (-)
f
e
Primary energy factor electricity (-)
The equivalent effectiveness of both air-to-air heat recovery units and EAHPs
for domestic hot water production, taking into account an increase in fan energy of
1,500 j/m
3
and a thermal effectiveness of 80 % for the HRU, an air change rate of
0.5 ACH, seasonal performance factor of 2.96 and 85 % efficiency for a con-
densing gas boiler, is shown in Figs.
5
and
6
respectively .
Air-to-air heat recovery is highly efficient with equivalent effectiveness of 50 %
and more in the northern part of Europe. EAHPs for domestic hot water production
are less effective in this region. In contrast to HRUs, their performance is higher in
the Mediterranean Basin, although it is still very low (equivalent effectiveness\0.4).
The performance of HRU is highly dependent on the efficiency of the fan. The
equivalent effectiveness calculated above takes into account fans with performance
levels at the top of the recommended default values by the European standard
(750 J/m
3
per fan). Measurements show that the performance in practice can range
over a broad spectrum. Lowering fan performance with one class (1,250 J/m
3
per
fan), to the mid-range of the CEN default values, reduces their profitability in the
major part of Europe, leaving only Scandinavia as an interesting region for their
application (see Fig.
7
).
When, on the other hand, a difference in fan power of only 500 J/m
3
is considered
(Fig.
8
.), which would correspond to the addition of a low pressure drop HRU in an
