I expect there are some suggestions I have missed, so please let me know if you think of any.
Saturday, 2 November 2013
Keeping Homes Warm in Winter at Minimum Cost
Here in the UK there is a lot in the news about soaring energy costs and the discomfort and risk to people who cannot afford to heat their homes adequately. Having had over fifty years’ experience, in a professional capacity, of trying to provide suitable internal environments for people in buildings I thought I would try to offer something useful by way of guidance on the subject.
In what follows I have tried to explain things in layman’s terms. First, let us consider the factors affecting human’s thermal comfort. These personal factors are:-
· Metabolism (all the chemical factors in a human being that result in energy production). In this respect we are all different.
· Amount and type of clothing. Another area where we are all different!
So doing some fairly vigorous exercise before going to bed will mean you will slide between the sheets feeling warm, whereas sitting around all evening watching the TV will lower your metabolic rate and mean that you go to bed feeling cold.
Similarly wearing warmer clothing which reduces the natural heat loss from your body will result in your feeling warmer. People in bygone days realised this and that is why nightcaps and bed socks were popular in unheated bedrooms in draughty houses. I wish I could get my wife to wear bed socks, instead she prefers warming her feet up on my legs!
Then there are the environmental factors:-
· Air temperature
· The surrounding surface temperature of walls, floors, ceilings and glazing
· Air movement (velocity)
· Relative humidity (in winter when internal relative humidity is generally low this does not have a significant effect so we will ignore it)
If the air temperature around your body is below your body’s surface temperature your body will lose heat to the air and you will feel cooler. If the surfaces around you are colder than your skin surface temperature your body will radiate heat to those surfaces and you will feel cooler. If air is moving over your bare skin then it will evaporate moisture from your skin and for this evaporation to take place energy is required and the energy comes from your body making it feel colder. You can prove this evaporation effect for yourself by licking the back of your hand and then blowing across the licked area. You will feel it go cold and your body will then have to warm it up again. The heat to warm your skin up has to come from your body.
Hopefully what we have looked at above is second nature to you and you dress appropriately keeping body parts covered (insulated) and you might consider wearing bed socks or even a night cap if your bedroom is cold at night.
Now let us look at the environmental factors, but before we do we must consider the two ways in which heat is lost from a room.
· If there is a temperature difference across a room surface (say a wall with 1 deg C outside and 21 deg C inside) then heat will want to flow from the warm side to the cold side. We call this a “fabric loss” because heat is flowing through the fabric of the room. We insulate walls, ceilings and floors to make it harder for the heat to flow through them. We double glaze windows for the same reason.
· If a wind or breeze hits an obstruction it results in high pressure on one side of the obstruction and low pressure on the downwind side. If there is an air pressure difference across a room (or a building) due to a breeze or wind then the high pressure air tries to reach the low pressure air by flowing round the obstruction or through it. We call the effect in the room a draught! The effect of the room air being changed by draughts is very significant in terms of heat loss particularly in older buildings when in windy conditions the whole volume of room air may be changed one or even two times per hour. All of this air has to be heated up to room temperature in order to maintain that temperature and the required comfort level. Also if there is a lot of air movement in a room due to draughts the occupants will feel cooler.
Given all of the above what are the practical ways available to help maintain comfort whilst reducing energy bills?
In terms of reducing the “fabric loss” the straightforward ones are:-
1. Insulate the room/building surfaces with cavity and roof insulation or surface insulation if a solid wall.
2. Use heavy curtains, preferably from floor to ceiling and keep them closed when possible. Close blinds especially at night.
3. Insulate behind radiators with foil faced polystyrene sheets.
4. Insulate the floor with thick carpets and underlay.
5. Turn off radiators in parts of the home that are unoccupied or if radiators are fitted with thermostatic radiator valves reduce the setting. Shut the doors to these areas.
6. I was always being asked which is best: do you turn your heating off when not required or is it better to keep it running continuously. In terms of saving energy you should turn it off (preferably onto a frost protection setting so you don’t get frozen pipes). Common practice, especially if you have young children, who kick their bed clothes off, is to turn the thermostat down at night or if you have a two zone system, only keep the bedroom zone running at night.
7. Warm air systems involving fans, heater batteries, ducts and grilles will heat up a home quicker than water systems so the pre heat period is shorter but they do result in more air movement so room temperatures usually need to be slightly higher than for a radiator system which does not have increased air velocities. Make sure the vanes on the grilles direct the warm air down otherwise you will have cosy temperatures at ceiling levels whilst being cold in the occupied area.
Regarding controlling infiltration a balance has to be struck between health and safety issues and controlling energy costs. Even if it were possible to eliminate air movement from outside completely it would not be desirable. Room occupants require oxygen to breath and the dilution of the carbon dioxide they breath out. Both require some fresh air entering the space. If the room is being warmed by a heat source that involves combustion actually in the room such as a gas fire, oil fired heater or even a multi fuel heater it is crucial that adequate fresh air ventilation to the room or appliance is provided. So don’t go blocking off vents specifically provided for combustion air supply. To reduce ventilation for combustion can result in the appliance producing a deadly gas called carbon monoxide. This colourless, tasteless and odourless gas makes one feel happy as a prelude to unconsciousness and death as it restricts the flow of oxygen to vital organs.
In terms of reducing the infiltration loss here are some practical suggestions:-
1. On a breezy cold day check windows, doors, skirting, etc. for obvious draughts using the back of a damp hand. You will only be able to feel the air coming in on the windward side of the building, so you need to repeat the exercise when the wind is blowing from other directions. Having determined where the draughts are you need to try to block or restrict the air path using an appropriate method. Some suggested methods are:-
a. For old metal casement windows with warped frames – clean off the window edges, put a release agent on one surface (washing up liquid) and a clear silicone sealant on the mating surface and close the window. Twenty four hours later the window can be opened again but by then the silicone should have made a perfect seal. If you forget the release agent you will probably never get the window open again!
b. Old wood sliding sash windows are more of a challenge. If you are looking for a cheap temporary fix, either wipe clean and tape over all the gaps or tape a polythene sheet over the whole opening. This is also the way to carry out a temporary fix if the window pane is broken.
c. Silicone seal any cracks or gaps around the frame and also check under the window sill.
d. With double glazed units check all the edge seals are in place and if not replace. Quality double glazed units usually come with “trickle vents” at the top. These could be closed during severe weather conditions but I usually like to see them left open to provide normal ventilation.
e. Pay particular attention to external doors, fitting draught strips if necessary and using the old-fashioned fabric sausages laid along the door bottom to block draughts.
f. During windy weather it reduces cold air infiltration of outside air if all internal doors are kept closed.
g. If you don’t have fitted carpets then check the gaps under skirting boards. If you cannot afford or cannot use a sealant gun then fold up strips of newspaper or card and force the strips into any gaps.
Finally, if you feel your thermostat is set too high, don't suddenly turn it down a couple of degrees, that will only upset other members of the family. Do a staged reduction over a week so they and you can acclimatize.