The
design element of a heat pump installation
is essential.
The task is to correctly size a heat pump to the demand of your property.
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The
demand of your property
In order to be able to match a heat pump up (with an output rating
in watts) to your property we need ascertain a figure in watts for
the demand of your property.
This figure will be unique to your property and will be calculated
in one of two ways.
The MCS standards outline two methods for calculation; the full calculation
method and the simplified method.
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The
full method for retrofitting heat pumps to
buildings built pre 2006
The simplified method for new build install and retro fit to post 2006.
The
reason for the split is that after building
regulation change of 2006 we know Modern
buildings require less power for heating
due to improved building methods and insulation
values. Although the methods are principally
the same, the simplified method makes more
assumptions due to the fact we can be sure
about how the building was built and to what
standards in relation to its heat retention
properties.
We
can conduct a survey on your property or
work from drawings if you have them. If not
we will come and visit in order to get things
right. Room by room we shall begin to calculate
the demand in watts for your property.
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From
these wattage results per room we can also
design an emitter type,
whether it be under floor heating, radiators,
or fan assisted radiators. By adding the all
the rooms together we then have a total heating
demand for the building in question. Now all
we need to do is add to the hot water demand.
The
hot water demand is based on the amount of
water we need to heat, which is based on
the size of the property, but also considers
occupancy level. MCS guidelines are to calculate
45 litres of hot water per person per day
and base the occupancy level of the house
at 1 person per bedroom plus 1
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For
example:
A 3 bed house would = 3 +1 x 45L =180L
Once we know the amount of water we have to heat we can put a figure
in watts to this and produce a total wattage demand for the property.
Sizing
the heat pump is a complex process and requires
the use of specially designed software in
order to produce accurate results based upon
the information we feed it. The survey and
design task is the most crucial part of the
whole heat pump installation. It is important
that the parameters we enter into the software
are true and accurate to the specific property.
Inaccuracies at this stage could result in
under sizing or over sizing the heat pump
which is not good.
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We
need to enter parameters and values on:
Degree
day data for your locality
Annual dry bulb temperature
Your average design temperature
U values (W/m²K)
Re-heat factors, based on re-heat speed required and by the level of
drop in temperature for the size of the house
Air Change Ventilation rates
Air Change Infiltration rates
Thermal bridging
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Once
all the relevant information is entered we
can match the job to a heat pump capable
of meeting the demand. From the matched heat
pump, we can enter further data into the
equation, taken from the manufactures data
sheets of the specific heat pump selected.
At this stage we are able to begin to put
some monetary figures to the stats produced
by the software.
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