2. What is space heating?
• Technical term for providing heat to
raise the internal environmental
temperature.
• Space heating can be achieved with
stand alone heaters, e.g. open fire
places: local heating
• More efficiently achieved with a
single heat source which distributes
heat round the building using a heat Royal
Agricultural
transfer medium: central heating College
3. Open fires: nice but… you need
lots, they are dirty, uncontrolled,
need constant fresh air
Central heating: one heat source
with a heat distribution system.
Complicated but controllable
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Agricultural
College
4. Why do we need it?
• Good question
–By careful design and
building management it is
almost possible to manage
without it.
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Agricultural
College
5. “Laws” of thermodynamics
• Heat flows from a hot body to a cold
body until the two are at equal
temperatures
– Understanding and controlling heat flow
is the key to space heating design
• Energy can neither be created nor
destroyed. It can only change forms
– Managing sources of energy, in
different forms, is the challenge of Royal
space heating design Agricultural
College
8. Basics of heat flow
Barrier to heat flow:
Insulation
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Agricultural
College
9. Controlling heat loss
• Reducing heat loss through the
building envelope reduces the need
for space heating.
• The thermal conductivity of a
wall, floor or roof enclosure is called
its “U” value
– Watts of power lost per square metre for
each degree centigrade temperature
difference: W/m2 OC Royal
Agricultural
College
10. U value in practice
Inside temp
10 OC
Difference in
1m2 of wall temperature between
inside and outside is
1OC
The amount of heat
travelling through one
m2 of wall is the U
value
Outside temp Acceptable U values:
9 OC Walls - 0.35 W/m2 OC
Roofs - 0.16 W/m2 OC Royal
Agricultural
College
11. U value calculation for a wall
plaster
• Thermal resistivity of 1 m2 for
blockwork
insulation 1mm thickness of each material
in wall found from published
data
• Resistivity multiplied by actual
thickness of materials
• All resistances added, plus
theoretical resistances for
boundary layers of air, to give
total thermal resistance of 1 m2
wall = R
• Reciprocal of R = 1/R = U value
• Must be 0.35 W/m2 OC or less
to satisfy current Building Royal
brickwork
Regulations Agricultural
College
12. Heat loss calculation
• Wall area = 500m2 U value = 0.35 W/m2 OC loss =175W OC
Roof area = 100m2 U value = 0.16 W/m2 OC loss = 16W OC
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Agricultural
College
13. Heat loss calculation
• Wall area = 500m2 U value = 0.35 W/m2 OC loss =175W OC
Roof area = 100m2 U value = 0.16 W/m2 OC loss = 16W OC
• The external “design temperature” in England is -1OC
The internal design temperature is what you want, say 22OC
Temperature difference is 23OC
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Agricultural
College
14. Heat loss calculation
• Wall area = 500m2 U value = 0.35 W/m2 OC loss =175W OC
Roof area = 100m2 U value = 0.16 W/m2 OC loss = 16W OC
• The external “design temperature” in England is -1OC
The internal design temperature is what you want, say 22OC
Temperature difference is 23OC
• Heat loss through walls = 175 X 23 = 4,025W
Heat loss through roof = 16 X 23 = 368W
Total heat loss = 4,025 + 368 = 4,393W approx 4.5KW
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Agricultural
College
15. Heat loss calculation
• Wall area = 500m2 U value = 0.35 W/m2 OC loss =175W OC
Roof area = 100m2 U value = 0.16 W/m2 OC loss = 16W OC
• The external “design temperature” in England is -1OC
The internal design temperature is what you want, say 22OC
Temperature difference is 23OC
• Heat loss through walls = 175 X 23 = 4,025W
Heat loss through roof = 16 X 23 = 368W
Total heat loss = 4,025 + 368 = 4,393W approx 4.5KW
• Disregarding floors, windows, doors etc. this house will need a
space heating input of about 4.5KW to keep it warm on a cold Royal
Agricultural
English winter’s day
College
16. Environmental heat input
• The space heating system is not the only
source of heat.
– 100W bulbs produces about 80W of waste
heat
– A sedentary person produces about 100W of
heat
– So if there are four people reading by the light
of 4 light bulbs, they are producing about
780W of heat, say roughly 1KW
• The boiler only needs to make up the
3.5KW difference Royal
Agricultural
College
17. The law of unintended
consequences
• We are being encouraged and required by
central governments to change heat
producing lights bulbs for lower energy
replacements.
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Agricultural
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18. The law of unintended
consequences
• We are being encouraged and required by
central governments to change heat
producing lights bulbs for lower energy
replacements.
• This saves around 1.5KW of electricity
needs for lighting in a house
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Agricultural
College
19. The law of unintended
consequences
• We are being encouraged and required by
central governments to change heat
producing lights bulbs for lower energy
replacements.
• This saves around 1.5KW of electricity
needs for lighting in a house
• In the winter we loose about 1.5KW of
heating which came from those bulbs
Royal
Agricultural
College
20. The law of unintended
consequences
• We are being encouraged and required by
central governments to change heat
producing lights bulbs for lower energy
replacements.
• This saves around 1.5KW of electricity
needs for lighting in a house
• In the winter we loose about 1.5KW of
heating which came from those bulbs
• In the winter we are all turning our boilers
up as a consequence, wiping out much of Royal
Agricultural
the intended energy saving. College
21. The basics of central
heating
• Fuel (chemical energy) is burned in
one location to raise the temperature
of a “heat transfer medium”.
• The heat transfer medium is moved
to a distant location where the heat is
needed through a “heat distribution
system”
• At the distant location the heat
transfer medium gives up its heat to Royal
Agricultural
the local environment. College
22. Energy sources
• Overwhelmingly space heating
energy sources are biological fuels
– Oil, coal, natural gas
– Bio mass, bio gas
• When they burn, they are combined
with oxygen to create water and
carbon dioxide, releasing heat
energy during this “exothermic
reaction” Royal
Agricultural
College
23. Central heat source
• The heat source is usually a boiler, where water
is heated
• It can be a heat exchanger where air is
heated, but these are less efficient and little used
unless there is a need for mechanical ventilation.
• Size of boiler chosen after carrying out heat loss
calculations and adding in predictable
environmental heating inputs
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Agricultural
College
24. Heat transfer media
• A transfer medium is a fluid which can
move heat from source to destination
• The desirable medium properties are
– high thermal capacity (it can hold a lot of heat
in a small volume)
– Ease of control
– Non-hazardous
• Water is ideal in most situations
• Steam is useful in large scale installations
• Air is much less efficient due to its low Royal
Agricultural
thermal capacity College
25. Heat distribution system
• Water: pipework, usually copper or
stainless steel if it needs to be strong
• Steam: high pressure, large diameter
pipes with integral insulation
• Air: large ducts with minimum
number of corners, interruptions or
leaks
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Agricultural
College
26. Hot water pipework
• Pipes should be insulated when they
pass through unheated spaces: roof
spaces, under ground floors
• Pipes are not usually insulated where
they pass through the heated part of
the house, as the heat they radiate
contributes to warming the house
• Pipe work must be kept full, must be
ventilated at high level and must Royal
Agricultural
have drainage taps at all low points College
27. Local heat emission
• Where the heat is needed, the
surface area of the pipework is
maximised to emit as much heat as
possible
• This can be done through
radiators, convector units or under
floor pipe networks
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Agricultural
College
28. Radiators
•Radiant heat and natural
convection currents
•Simple and largely fail safe
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Agricultural
College
29. Convector units
•Air is blown over hot water pipes by a fan.
•Very hot water can be used, which is efficient
•Can be combined with ventilation using outside air intake. Royal
Agricultural
•Can be served by chilled water pipes from an air conditioning unit
College
•Noisy but very good where intermittent use is needed
30. Under floor heating
• Entire floor is a radiator
• Expensive to install
• Efficient in areas where constant
heating is needed,
• Inefficient for intermittent heating
• Insulation must be placed below
hot pipes
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Agricultural
College
31. System control
• Electronic control systems have increased
the efficiency of heating systems more
than any other technology
• Time switches on boilers
• Thermostats for radiators in rooms
• Zoning of buildings with separate controls
for each zone
• Remote control via mobile phones/internet
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Agricultural
College
32. District heating
• Central district boiler
• Steam pumped to
individual buildings
• Heat exchangers in each building
heats water for radiators in the
building
• Can be highly efficient in urban
locations for large developments
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• Loss of personal control Agricultural
College
33. Professional advice
• Space heating systems are amongst the
biggest consumers of fossil fuels and
biggest contributors to green house gas
(CO2) emissions nationally
• The design of any new building should aim
to reduce the need for space heating to a
minimum
• In all but the simplest installations, the
systems should be designed by a qualified
services engineer to minimise their Royal
environmental impact Agricultural
College
