16 glossary of terms – Grant Products HPAW155 User Manual

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Glossary of T



16 Glossary of Terms

The word “efficiency” is defined as the
ratio of useful heat output to energy
input. For example, if we use 1 kW of
energy to produce 500W of heat it is
deemed to be 50% efficient.

Loosely speaking, when a system’s
energy is divided into its “useful) energy
(energy that can be used, for example,
to push a piston), and its “useless
energy” (that energy which cannot be
used to do external work), then entropy
can be used to estimate the “useless”,
“stray”, or “lost” energy, which depends
on the entropy of the system and the
absolute temperature of the

The COP or ‘Coefficient of
Performance’ is found by dividing the
useful heat output by the energy input.
For example; a heat pump that
produces 4 kW of heat for 1 kW of
input power has a COP of 4.

Seasonal Performance Factor is similar
to COP, but is an average figure taken
over the year. It is usually lower than
quoted COP figures due to the need in
some cases for additional heat input
during very cold periods.

This is wherever the heat is being
extracted from e.g. the outside air or

A term used to describe radiators or
underfloor heating. This is the
component that ‘emits’ the heat into
the building.

The working fluid within the heat pump.
It evaporates in one part and
condenses in another. By doing so,
heat is transferred from cold to hot.
This fluid is sealed in and will not
degrade within the life of the heat
pump. Refrigerant handling should only
be carried out by persons qualified to
do so.

Heat Exchanger
A component that allows the
transference of heat from one circuit to
another without the two circuits mixing.
Two heat exchangers are housed within
the heat pump, one for the hot side (the
condenser which transfers the heat to
the heating circuit) and one for the cold
side (the evaporator).

Geothermal is often mistakenly used to
describe a ground source heat pump;
proper geothermal energy is where the
energy from the earth’s core is able to
make its way near to the surface,
usually using hot water. In the UK there
are only a couple of sites where this
type of energy extraction is feasible as it
requires holes in excess of 2km deep.

Buffer Tank
This is simply a large water cylinder that
is used, so we are told, to improve the
efficiency and durability of a system.
In fact, it reduces the number of
stop/starts the compressor makes.

Heat Pump Rating
A heat pump is given a kW heat output
rating. This value will vary depending on
the working temperatures. The electrical
power input will be typically between a
half and a quarter of the heat output.

A monovalent system is one where all
of the energy required for the heat load
of the building is available from the heat

Bivalent systems are those which
require an additional source to meet the
buildings heat load.

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