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Radiation suit
This month, heat pump specialist Bob Long looks at choosing
the most effective emitter for the job
H
aving completed an accurate heat
load analysis of your project, and
selected a suitable heat pump, the
next step would be the choice of emitter,
influenced by considering a number of factors.
Panel radiators
The most common type of emitter is the panel
radiator and would generally be reliant on
water flow temperatures anywhere between
65 and 80°C.
This temperature range is not readily
achievable by heat pump technology, and
although some manufacturers are offering
high temperature units, the operational
economics will be compromised by the higher
temperatures.
Clearly, a retrofit scenario that reduces
the operating temperature of the radiator will
not deliver the required amount of energy to
heat the space, without increasing the size
of panel radiator. In some installations this
can be achieved but wall space is often the
limiting factor.
Further consideration, when retrofitting
an existing system, should be given to the
water flow rate. A defined volume of water,
transported around the system at 70°C, will
contain more energy than a similar volume of
water at 40°C.
Similarly, the circulating pump capacity
must be increased to ensure delivery of an
adequate amount of energy. When increasing
pump capacity, further consideration should
be given to pressure drop which will increase
proportionately with higher velocity of water
flow.
When deciding if a retrofit is the best way
forward, all these factors should be considered,
before embarking on a complicated solution.
For a new installation, there are basically
three emitter type-options available, fan/coil
unit, underfloor pipe matrix, or panel radiators.
Fan/coil units
Fan/coil units are designed to be very
compact yet have large capacity. It is
important when selecting a suitable unit that
the sales literature clearly states the output for
the intended water temperature.
Fan/coil units can be wall mounted,
where the exterior finish often benefits from a
range of visually pleasing styles, or the fan coil
units can be located in ducts, which direct
and deliver the warm air to various strategic
outlets.
The fan coil unit method of energy
delivery in perhaps the most versatile of all
heat emitting systems available. A suitably
sized fan/coil unit can deliver at least the
same amount of energy as the most efficient
underfloor system, and is suitable for new-
build and retro-fit installations.
Underfloor heating
Underfloor heating is often an attractive
choice in new-build projects as it provides
good heat emission at relatively low water
temperatures, and the actual heat exchanger
is out of site. The only visible items are
probably going to be the supply and return
manifolds, but these are usually located in a
cupboard.
The heat load of the particular room plays
a great role in the selection process, as does
the physical size of the room.
The total heat load of quite a large room
could probably be accommodated with a
single fan/coil unit, but would not promote
an even air pattern, and maybe leave one
part of the room at a lower temperature, so it
is important for the selected unit to not only
match the heat load required, but to dissipate
the energy evenly. This may require two or
three fan coil units, each supplying one third
of the required energy, but producing a much
more even temperature, than a single emission
point.
There are further considerations when
choosing emitters, such as water flow rates,
pipe diameters, pressure drop, pump selection
etc. But a most important consideration not
yet mentioned is, of course, your client’s
lifestyle requirements, and the influence this
has on the heating system’s overall design.
www.renewableenergyinstaller.co.uk | 15