Page 39
3.5 Defrosting
Due to the nature of the heat pump operating cycle, frost and ice may build-up on the evaporator.
The unit senses this build-up and then performs a defrost cycle to get rid of this ice. As a result,
the ice is melted and collects in the drip tray. The trip tray is heated to prevent this water from
refreezing. Holes in the bottom of the drip tray allow the water to exit the heat pump.
Adequate provision should be made to prevent condensate from collecting around the units. A
soak away underneath the unit or drip tray should be used as deemed appropriate to the site.
3.6 Air Vent
Each unit features a manual air vent located at the top of the unit (internal on some models,
external on others). This is to allow air to be removed from the unit when it is filling.
NOTE: For models with an internal manual air vent, a piece of piping must be fitted to the
air vent before opening it to ensure no water is sprayed onto any electrical components in
the casing.
3.7 Buffer tank
In order to perform the defrost cycle, the air source heat pump runs in reverse mode. The defrost
cycle takes a small amount of heat from the heating system and uses it to melt any frost or ice
which may have formed on the appliance’s evaporator. Frost or ice which has formed on the
evaporator will interfere with the operation of heat pump and it is therefore vital that it is thawed
to remove it. The appliance will defrost regularly in order to maintain its performance. To ensure
the availability of sufficient heat for the purposes of defrosting, it is recommended that an in-line
buffer tank of appropriate size is incorporated on the return heating pipework to the appliance. An
in-line buffer tank accessory is available separately from Warmflow (AS01 – 18l capacity, AS02
– 30l capacity, AS03 – 50l capacity).
If an in-line buffer tank is not incorporated into the installation, a calculation must be performed to
determine the circulating volume of water which is available to the appliance for the purposes of
defrosting. The minimum circulating volume required for each appliance model is given in Table
6. The calculation below must be used to calculate the actual circulating volume. This actual
volume must always be equal to or greater than the minimum circulating volume indicated for the
appliance in Table 6 and must also be recorded in the Installation & Commissioning Certificate,
see Page 70.
In all cases an open circuit must always be maintained to allow defrosting to occur.
Model
Volume
(l)
See Table 1 for
Model Fluid
Content
+
Total Pipe
Volume
(l)
See Appendix A
for guidance
+
Total Emitter
Volume *
(l)
See Appendix A for
guidance
=
Actual
Circulating
Volume
(l)
*
= Radiators without TRVs, open UFH loops, etc.
3.8 Bypass Valve
In order to provide sufficient flow rates and to facilitate defrosting, it is essential that the heating
circuit can always achieve a minimum flow rate of at least 10 litres per minute even when no
zones are calling for heat. This can be achieved by fitting a bypass between the flow and return
or by leaving a number of zones/radiators permanently on. This will significantly reduce short
Summary of Contents for A Series
Page 36: ...Page 34 Figure 24 AS02 R32 Casing Dimensions Heating Connection Locations FRONT SIDE TOP...
Page 40: ...Page 38 Figure 26 Heating DHW Schematic Figure 27 Heating Only Schematic...
Page 70: ...Page 68 7 APPENDIX B WIRING DIAGRAMS...
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