Energy Performance
Certificates
Heating
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LEVEL 3
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– HEATING SYSTEMS
There are many varied forms of introducing heat to
occupied areas, this guide will detail the most
common forms of heating system likely to be found
in buildings suitable for a Level 3 assessment.
To have an improved understanding of the types and
operation of systems, some definitions require to be
addressed
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Direct & Indirect Heating Systems
Direct Systems
These are where the fuel is burned directly to give
heat output, for example gas fired unit heaters,
electric panel heaters, gas fires etc.
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Indirect Heating Systems
This is where the fuel is burned by a boiler or other
heat producing device to heat another media (water /
air) which is then transported to a terminal device to
give a heat output (radiators, fan convectors, grilles
etc.).
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Radiant and Convective Heating
Convective Heating
Convective heating systems use the movement of
warm air to transfer heat. This air movement can be
induced by natural convection or by the use of fans,
for example via:
• Fan convectors
• Floor or ceiling-mounted unit heaters
• Central air-handling plant.
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Radiant Heating
Radiant heating systems use infrared radiation to
heat the building’s occupants and its fabric directly,
without the need for warm air as a transfer medium.
They are particularly useful for heating large
volumes with high ceilings, typical of industrial
buildings. Radiant systems can also provide local
‘spot heating’, and are also particularly efficient in
buildings with high air change rates.
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Boilers
There are many types sizes and outputs available using various
fuel types to suit every type of Low Pressure Hot Water (LPHW)
application, whether these are simple singular wall mounted
applications to multiple floor mounted installations, the same
process is occurring, Water is being heated and circulated to
provide useful heat.
The boiler provides an indirect source of heat to be distributed
through pipework systems which is then discharged to the
space by means of radiators, convertors radiant panels or
similar. The most common forms of heating devices likely to be
assessed are described later within the training course
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Atmospheric vs. Condensing
A condensing boiler is a high efficiency modern boiler that
incorporates an extra heat exchanger so that the hot
exhaust gases lose much of their energy to pre-heat the
water in the boiler system. When working at peak efficiency,
the water vapour produced in the combustion process
condenses back into liquid form releasing the latent heat of
vaporisation. The efficiencies of this type of boiler are fully
dependant on the flow and return temperatures of the media
heated.
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Wall Mounted Boilers
This type of boiler is not dissimilar to what is likely
to be found In a domestic home, however these
generally have a higher output and will have
components such as expansion vessels and pumps
mounted remotely from the boiler itself.
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Wall Mounted Multiple Boiler Installations
This type of installation has become more common over the
past few years and is generally used in larger applications
where one boiler is not capable of providing the required load,
or where a back-up is required.
These units can be controlled on a duty / share operation which
will be covered in further detail under the controls section
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Wall Mounted Boilers
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Floor Mounted Boilers
Floor mounted boilers will generally be found in older
developments or where larger heat outputs are required. These
can also be installed in multiple arrangements to increase
loads and provide back-up facilities
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Multiple Boilers
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Boiler Efficiencies
Care should be taken when assigning boiler efficiencies to
produce the Energy Performance Certificate. Manufacturers will
advise efficiencies well in excess of 90%, and although this is
achievable it can only be obtained under specific flow and
return (F&R) conditions, especially in the case of condensing
boilers.
Follow the LATEST conventions
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Distribution Systems (WET SYSTEMS)
Radiators
Although delegates on this course will have knowledge of
domestic wet heating systems using radiators, the following
diagrams detail more complex installations to be found in
commercial premises-
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Radiators and convectors are the principal means of heat
emission in most buildings. Less popular alternatives
include exposed pipes and radiant panels for use in
warehousing, workshops and factories. where appearance
is not important. Embedded panels of pipework in the floor
screed can also be used to create 'invisible' heating, but
these have a slow thermal response as heat energy is
absorbed by the floor structure.
Despite the name radiator. no more than 40% of the heat
transferred is by radiation. The remainder is convected, with
a small amount conducted through the radiator brackets
into the wall.
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Radiant Wet System
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Originally. radiators were made from cast iron in three forms:
Hospital. Column and Panel. Hospital radiators were so called
because of their smooth. easy to clean surface, an important
specification in a hygienic environment. Column radiators vary
in the number of columns. The greater the number, the greater
the heat emitting surface.
Cast iron radiators are still produced to special order. But
replicas in cast aluminium can be obtained. Cast iron panels
have been superseded by pressed profiled steel welded panels.
These are much slimmer and easier to accommodate than cast
iron in the modern house. In addition to the corrugated profile.
finned backing will also increase the heating surface and
contribute to a higher convection output. Pressed steel
radiators are made in single. Double and triple panels.
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Radiant & Convector Skirting Heaters
Radiant and convector skirting heaters are unobtrusive at
skirting level and provide uniform heat distribution throughout
a room.
Natural convectors have a heating element at a low level within
the casing. This ensures that a contained column of warm air
gains velocity before discharging to displace the cooler air in
the room. Fan convectors may have the heater at high level
with a variable speed fan located below. In summer. the fan
may also be used to create air circulation.
Overhead unit heaters are used in workshops to free the wall
space for benches, machinery. etc.
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A variation may be used as a warm air
curtain across doorways and shop
entrances.
Individual unit heaters may have a
thermostatically controlled inlet valve or a
bank of several units may be controlled with
zoning and diverter valves to regulate output.
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Radiant heating systems use infrared radiation to
heat the building’s occupants and its fabric directly,
without the need for warm air as a transfer medium.
They are particularly useful for heating large
volumes with high ceilings, typical of industrial
buildings. Radiant systems can also provide local
‘spot heating’, and are also particularly efficient in
buildings with high air change rates
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Radiant heating systems offer the following benefits relative to
convective types and are often the first choice for industrial
buildings:
Energy consumption can be lower, as a result of:
Generally lower air temperatures
Reduced stratification at high level
Directional output delivers heating directly to where it is
needed
Rapid warm-up
Responsive control
No air movement.
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Radiant Panels Served by Boiler
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Underfloor Heating Systems
Underfloor heating is far from a new concept, it was first used
by the Romans whose dwellings were constructed with voids
through which air, warmed by an open fire, would pass thus
heating the structure.
In the more recent past electric heating elements were buried
within floor screeds. These were heated over night using
'cheap rate' electricity. However, the building would overheat
during the day but in the evening, when heat is generally
required, no further heat was available.
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Utilising today's modern multilayer pipes, control systems and
high efficiency boilers, the underfloor heating systems of today
are extremely comfortable and controllable.
Radiators are no longer needed so giving more room space.
The heat is more evenly distributed and dust is not circulated.
Underfloor heating from the whole floor area of the house
gently warms the air above, eliminating cold spots.
The warm air convects from the floor surface losing
approximately 2 degrees centigrade at 2.0 meters above the
floor.
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Independent tests reveal that the most acceptable indoor
climate is one in which the floor temperature ranges
between 19-29°C and the air temperature at head level
ranges between 20 and 24°C.
With radiator or convector heating systems a vertical
temperature gradient is produced; colder at foot level
than at the head. Underfloor heating has made it possible
to reduce energy consumption by using low water
temperatures. These systems, based on the development
of complex and very high quality plastic pipe, such as the
multilayer pipe, now account for over 60% of some
European heating markets
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Underfloor heating systems are suitable for both
domestic and commercial applications. It has a
particular advantage in public areas where exposed
hot surfaces can be dangerous.
Gas, oil or solid fuel boilers can be used as the
source of heat for any underfloor heating system.
Condensing boilers being particularly suited as the
operation of underfloor heating systems allows them
to operate in their most efficient manner.
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It is possible to combine both underfloor systems with radiator
systems. For example, the ground floor could be heated by an
underfloor system whilst the 1st floor is heated using a wet
radiator system or radiators can be fitted in the bathroom and
lavatory in homes where the main system is underfloor heating.
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Ducted Warm Air System
Warm air can be used as an alternative to hot water in pipes.
There are no obtrusive emitters such as radiators. Air diffusers
or grilles with adjustable louvres finish flush with the ceiling or
floor. The heat source may be from a gas, oil or solid fuel boiler
with a pumped supply of hot water to a heat exchanger within
the air distribution unit. The same boiler can also be used for
the domestic hot water supply. Alternatively, the unit may burn
fuel directly, with air delivered around the burner casing.
Control is simple using a room thermostat to regulate heat
exchanger and fan.
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Positioning grilles in doors is an inexpensive means for
returning air to the heater. but a return duct is preferred. Fresh
air can be supplied to rooms through openable windows or
trickle ventilators in the window frames. If rooms are
completely sealed, fresh air should be drawn into the heatinq
unit.
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Distribution Systems (DIRECT RADIANT)
Gas fired radiant tube heater
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Distribution Systems (DIRECT RADIANT)
Gas fired radiant tube heater
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Gas fired plaque heater
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Gas fired plaque heater
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Electric Quartz radiant lamp: Efficiency 100% (1.0)
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Electric Quartz radiant lamp: Efficiency 100% (1.0)
Follow LATEST conventions
• Losses are in power station and transmission
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• Distribution Systems (DIRECT CONVECTIVE)
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• Distribution Systems (DIRECT CONVECTIVE)
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• Floor Standing Unit Heater
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Floor Standing Unit Heater
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Efficiencies
Generally direct fired gas or oil appliances have
good efficiencies and most of the new modern types
are listed on the ECA (Enhanced Capital Allowance
Scheme).
However, actual percentage efficiencies should be
sought from manufacturers data, if this data cannot
be collected, the default values within the SBEM
interface software should be used.
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De-Stratification Fans
With any conventional heating system, natural
convection increases the temperature gradient.
This results in the ambient temperature at the apex
of the roof being greater than the required design
temperature in the occupied zone at floor level
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By using a system of destratification fans, the hot air in the roof
space is directed down to the required area, thus reducing the
heating load
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These unit are operated by a thermostat to switch the fans off
or on dependent upon the temperature settings of the
thermostat and the internal room temperatures. These fans are
also useful in summertime to reduce cooling loads.
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