Heating - Choice of System - Page 1
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Factors that Influence the Choice of
Heating System
The
following is a list of some of the factors, which influence the type of heating
system:
1. Cost
Installation cost - Pipes are cheaper than ducts.
Running cost - Oil,
Coal or Gas or Economy 7 electricity or wood products.
Life Cycle costs - Reliable
system, long working life e.g. Cast Iron boiler.
Maintenance costs - Coal
as a fuel may be expensive to maintain. Other systems have less maintenance
requirement.
- Gas burns cleaner than oil and there is less soot to
clean out of a gas boiler and flue.
2. Fuel or Heat Source
There is a
choice in most countries between;
Oil, Coal,
LPG (Liquid Petroleum Gas), natural gas, Economy 7 electrical heating, Ordinary
Rate electrical heating, Wood products.
In some
countries peat, lignite or soft brown
coal is available.
The
economics of burning this on a large scale would have to be considered.
There are
various grades of oil, some of the more
viscous (heavier) oils are cheaper but require specially heated burners and
heated pipes.
Calculate
the less expensive option.
3. Safety
Some open
gas and coal fires and paraffin heaters have a poor
safety record.
Ensure all
apparatus is approved and meets standards and regulations.
Systems
that use steam should be inspected annually to
ensure that pressure vessels are safe and safety valves function.
4. Type of Building
There are
many types of building encountered in building services, the following are a
few suggestions:
Large areas
benefit from the quick warm-up of air heating.
Ventilation
systems with ductwork require ceiling void space.
For
Warehouse radiant heating may be a
suitable option since the air temperature need not be high.
Hospitals
require clean environment; thus filtered
air heating may be necessary, usually in a full air conditioning system.
Museums and
Archive Stores require constant control
of room temperature and humidity - air-conditioning may be necessary.
In some
buildings it is difficult to run services through e.g. stone walls, solid
concrete slabs, therefore electrical
heating may be used.
In
buildings with large occupancy a
ventilation system may be necessary to provide adequate fresh air for occupants
e.g. concert hall, auditoria.
In
buildings with high heat gains
air-conditioning may be necessary to maintain comfort levels.
Schools
have limited wall space so underfloor heating
or low temperature ceiling heating is sometimes used.
In some
buildings like nursery schools and nursing homes, if radiators are utilised, it
is advisable that low surface temperature radiators
are used.
In wet
areas like shower rooms and bathrooms underfloor
heating has an advantage in that it keeps the floor dry.
Some
buildings like churches may be
intermittently used so electrical heating may not completely ruled out.
High
temperature roof mounted quartz electric heaters have been used in this
type of building.
Prestigious areas may have full comfort air conditioning to reflect the
importance of the room e.g. board room.
5. Comfort
To maintain
adequate comfort conditions a controllable heating system will be necessary
e.g. automatic controls on oil or
gas-fired system or electrical heating system.
A solid fuel system cannot be easily controlled.
Wood
pellet boilers are
automatically controlled in the same way as other boilers.
A
comfortable heating system may incorporate some radiant
heating as well as convective.
Radiant heating
is not always achievable but radiators produce about 70% convective and 30% radiant
heating.
It may be
difficult to obtain comfort levels in an office if a purely radiant system is
used such as radiant panels so a mixture of convective
and radiant heating is desirable.
If noise
levels in a room such as a Library are to be at a minimum then fan convectors are not a good option and some other
quieter form of heating is better such as radiators, underfloor heating,
natural convectors or a radiant ceiling.
6. Power Supply
When using
electrical heating there must be an adequate electrical
power supply.
For a large
building or group of buildings this may mean a new or upgraded electrical sub-station has to be provided.
7. Space
Plant
requirements; room for plant and equipment, storage space for fuel.
Some
construction methods do not provide adequate space for large plant e.g. a trussed roof space is awkward to use for services
plant.
A basement
plant room can be compromised if the area is prone to flooding.
An
apartment or flat may not have sufficient room for water
tanks or boiler.
An inner
city building may have no space for fuel storage therefore electrical heating could be the
option if natural gas in unavailable.
8. Vandalism
Some
systems do not stand up to abuse.
Keep walls
clear of pipes in some buildings e.g. prisons, detention centres.
Use steel instead of copper pipework in exposed
areas.
Some
emitters are not robust e.g. economy 7 electrical heaters.
Heavy-duty radiators can be used e.g. cast iron.
Some types
of steel panel radiators are suitable
for flush fitting in a wall if a recess is provided.
Prison
cells can be heated with surface mounted low-level
pipes.
Temperature
sensors should be protected.
9. Security of Supply of Heat Source
Some fuels
at certain times may be liable to unsecured
supply e.g. oil prices can fluctuate during a
It may be
advisable to have a dual fuel system
so that burners can easily be changed over to burn the cheaper or more readily
available fuel.
Alternative
sources of energy are not always secure e.g. the wind doesn't always blow on a
wind farm.
The sun
doesn’t always shine if the system relies on solar
panels.
A hybrid system is more secure or back-up boilers can
be used.
10. Let Buildings
Most
landlords prefer the tenant to look after payment of their own heating bills.
Individual meters for gas or electricity in a block of flats
means that the tenants are responsible for the payment of bills.
In a large
office building with several tenants, economy 7 electrical or natural gas
heating may be used otherwise it is difficult to divide up a wet heating system
serving a whole building so that suitable payments can be made for heating.
Some heat meters are expensive and not always
reliable.
Some
billing arrangement needs to be in place to charge tenants for heating.
11. Environmental Issues
The products
of combustion of oil, coal and gas pollute the atmosphere.
Coal is
probably the worst offender since
carbon dioxide contributes to the greenhouse effect and sulphur dioxide causes
acid rain.
Smoke
causes urban smog and soot and ash add to the problem.
Oil
produces contaminants to a lesser extent and gas is probably the best of the
three.
Using
electricity is of little benefit because power stations burn fuel to produce
electricity or use nuclear fusion or fission as a source of heat which has its
own impact on the planet.
A totally 'green' source of heat may be wind power or wave
power or solar energy if you live in an area with plenty of sunshine.
Wood
products such as pellets
have zero Carbon emission since trees can be
replanted to replace this fuel source.
Wood
pellets boilers use pellets
from an on site storage facility.
12. District Heating
If un-used hot water from a power station or other industrial
plant is utilised for domestic and commercial heating then the system could be
designed to utilise this cheap source of energy.
13. Outside Conditions
In some
countries the outside temperature in winter is very
low i.e. minus 10 decC to minus 30 degC.
Because of
high emitter output requirements it may be better to heat with warm air as opposed to hot water.
In some temperate climates it is not worth the expense of
having a wet heating system and electrical heaters are suitable for occasional
use.
If a
building has high internal heat gains,
even in winter, then an electrical heater battery can be used in the air
conditioning system instead of a wet system if occasional
use is envisaged.
In rooms or
buildings, which have an intermittent net heat gain and heat loss, then a heat pump may be used.
A typical
use of heat
pump is in a heavily glazed building where in a sunny period the
heat pump is in cooling mode and if the outside temperature drops the heat pump
switches to heating mode.
14. Fluctuating Heat Demand
In some
buildings the demand for heat fluctuates widely throughout the day.
To meet
this demand economically, a modular boiler
system is a good option.
This means
that the required number of boilers is automatically switched on to meet the
demand.
In some
circumstances it is recommended that condensing
boilers can be used to meet the base heating load and non-condensing
boilers can be utilised to meet the peak loads.
Condensing
boilers squeeze more energy out of the fuel by taking extra heat out of the
flue gases with a heat exchanger, Efficiency can be 98%
15. Appearances
In some
rooms or buildings the designer may require the heating system to be totally hidden e.g. underfloor heating, heated
ceiling or air heating.
In some buildings the
designer may wish to make a feature of
the heating system or heat emitters e.g. warm air ductwork system painted a
bright colour in a swimming pool hall or sports hall, Victorian cast iron
radiators in a period building.
16. Industrial Waste Heat
In some
factories heat is available from the process e.g. condensate or steam available
as a by-product.
Steam
can be used directly in a warm air heater or ‘stepped’ down to low temperature
hot water in a heat exchanger for use in the normal L.T.H.W. emitter system.
There are
many ways in which waste heat can be utilised to pre-heat water or up-grade in
heat pumps for further use in space heating.
Hot water
from Combined
Heat and Power (CHP) systems can be used to heat a factory or sold
to neighbours.