We’re following on with Tracy and Roger and their apartment being
expensive to heat.
As their apartment has very high humidity levels the cost of heating will be higher than it need be.
To heat anything be it a brick, a saucepan, a kettle full of water, they all require energy. However the amount differs with each material or liquid. Water for instance requires a lot of energy to heat it but it also holds heat reasonably well.
If the weather is very hot and humid our body sweats to try and keep us cooler. The idea is the sweat being water will absorb heat energy and cool the surface of the skin. Conversely if we are feeling cold our body stops producing water vapour and raises the fine hairs that cover the body in order to trap air from moving. Still air is a good insulator.
The bottom line is water and wet things take a lot of energy to try and raise the temperature. Dry air takes far less energy to heat it. Tracy and Roger have, or rather had a very humid apartment that made everything damp. Even the air was full of water vapour so it took a lot of energy to raise the air temperature.
Drying the whole apartment out with the dehumidifier mentioned in the previous blog has made the air will be easier to heat. The air is in contact with most things in the apartment so it will raise the temperature of everything it is in contact with until it is all at the same temperature.
The problem is a bit like a bucket with a hole in it. As you try filling it with water it pours out the hole. The same thing happens to materials. Some materials are dense therefore they have lots of atoms. Heat is the result of the atoms colliding so if there are a lot of them then the amount of energy required to make them all move is a lot.
Dry air hasn’t got many atoms so it will heat up quickly and easily. The gas molecules can freely move about changing the density of the air. The wall in contrast is dense concrete so it has billions of molecules that can vibrate but not move about as such, solid.
So the air warms up easily and tries to make the wall the same temperature. The amount of energy in the air is not enough to heat the wall quickly so in effect the air cools down to the wall temperature. If the wall is damp it will take even more energy to heat it.
However when the wall temperature does increase albeit very slowly it will be easier to keep the air temperature higher. In other words if the heating is on and the walls warm up they will then act as a heat store so the air in the room doesn’t need as much energy to remain warmer.
That is the argument as to whether it is better to leave the heating on low all day or better to turn the heating off when you are not at home.
We could do some calculations to show it is cheaper to turn the heating off when you’re not at home. In contrast we could also do a set of calculations to show it is actually better to have the heating on low whilst you are not at home.
Easy; It all depends upon what is in the apartment, what the
moisture content is in all of the materials including the relative humidity of
the air. Same apartment when it is damp with a high humidity will cost more to
heat than a dry apartment with low relative humidity.
Bottom line; Heating air with an electric blow heater is quick especially if the RH is low. However the heat will very quickly cool down as the air comes in contact with all the materials such as the walls, furniture and furnishings. It is and expensive and inefficient way of heating a room or the apartment.
A more efficient form of electric heating is to heat a material directly and let the material heat the air by radiated heat and convection currents. There have been various versions of heater ranging from a cabinet of bricks that required a lot of energy to heat them but made use of cheaper electricity produced during the night and a booster during the day. The electricity went through a different meter known as the Economy 7 meter. The thermal stores were both bulky and very heavy and known as ‘storage heaters’.
The principle was to utilise cheaper electricity at night and give out heat by radiation and convection. The wiring required was heavy duty and too much to run off the normal ring circuits of the property.
As a heating system they are not very efficient and cannot be regulated. If the storage heaters had been set at a specific temperature and the weather changed to a warm period the storage heaters could not be turned down. Conversely a quick very cold period and the storage heaters could not easily respond.
Tracy and Roger have another type of electric heater, not a storage one. Their system is basically a metal cabinet with a long wire as an open coil that is attached to a plastic board. It’s a bit like a bread toaster in that the wire (element) becomes red hot and the radiant heat warms the air around it. They are termed ‘convector heaters’.
To make it more efficient a rotary cylindrical fan gently blows the air across the heating element and out into the room. There are three individual elements that can be operated depending on the heat required. The heater cabinet has a thermostat that monitors the air near the heater and regulates the amount of energy being used by turning it on or off.
That type of heating unit is expensive to operate however it will very quickly warm the air in a room. The amount of energy the heater will use means it can be operated safely from a 13amp socket on a typical ring main. (Max 3kW)
Other designs of heater include oil filled radiators. The principle is to directly heat oil in a sealed container. The oil requires a lot of energy to heat it but as a result will slowly cool down therefore providing a steady flow of heat into the room.
The immersion heating elements enable the required amount of heat to be applied to the oil and a thermostat enables a desired air temperature to be maintained.
The problem with the oil filled radiator is the time required to heat the oil. To overcome the issue some models have a timer that can be set so that the heater will operate only during a set time period.
Designs have become more efficient and therefore smaller heaters can produce more heat. The increase in efficiency has been achieved by using ceramic sheets that are directly heated by an electrical element. The material is dense therefore can be made very thin and still give out enough heat.
Tracy and Roger’s apartment has a dense concrete ceiling which is the floor of the apartment above. Any heat rising will be absorbed by the dense concrete as opposed to building up within the room. Apart from insulating the ceiling there is not much than can be done to improve that issue.
The walls are poorly insulated. Possibly cavity wall construction in some apartments but alas not their one. The walls are literally solid panels of dense concrete that have been plastered over. A layer of insulation could be attached to the wall which would improve the thermal insulation.
As it is, the dense concrete walls literally soak up any heat, they’re heat sinks. When the room heating of is off the temperature of the concrete will drop down to 15°C or slightly lower. That means the air when it is heated again it will need to raise the wall temperature to about 21°C = very costly. If the outside temperature is really cold plus the natural air turbulent of living in a high rise building the wall temperature can significantly fall.
Realistically to reduce the heat loss through the walls is not economical. Various companies state their products will ‘reduce heat loss’, ‘improve thermal insulations’ and so on.
I haven’t named the product or manufacturer however here are some of their claims:
“ product that utilises technology originally developed for aerospace ”. – Hmmm? I wonder what technology they are referring to?
“stops heat escaping through walls and ceilings” – impossible. Nothing can do that.
“minimises condensation, mould and damp, and reduces your energy bills too” – if the wall temperature has not changed and the relative humidity has not changed then the incidence of condensation will not change.
“both the cooling effect of the wall and cold air currents in the room created by the differential temperature zones within a room” – let’s make it sound scientific so it must be true. It certainly cannot change the ‘cooling effect’ of a wall. If the wall has not changed then neither has the thermal characteristics.
What is a ‘differential temperature zone?’ More gobbledygook.
There are several other claims made as to how wonderful their product is at reducing noise.
The product has no independent laboratory test certification or British Standard Kite Mark.
The website reviews mention how ‘the room feels warmer’ . Yes that might be true. ‘Feels warmer’.
If you have a sheet of expanded polystyrene, perhaps packing materials from something you have bought. Put your hand on it and it ‘feels warm’. What is actually happening is the heat from your hand is being reflected back so your hand doesn’t lose so much heat.
The process it termed conduction. A material or substance that conducts thermal energy (heat) will absorb the energy quickly and our brain determines it is a cold surface, material, liquid.
If the material is a very poor conductor of thermal energy the heat lost from our hand is minimal and the brain determines the item is warm.
Try a simple experiment. Place your hand on a metal table or chair leg and the other on the soft material of the seat or chair back. Which ‘feels warmer’? They are both the same temperature as the air that is in contact with them. Check it with a thermometer.
That is all that is happening; the wall isn’t any warmer - only ‘feels warmer’.
A thickness of 3.5mm polyester isn’t going to do much at all.
Back in the 1970’s companies claimed their expanded polystyrene ‘wall veneer’ would save £ on heat loss. It was about 2mm thick. They also claimed it made the wall ‘feel’ warmer and people believed them.
Heat energy moves through materials by causing the atoms / molecules to vibrate and collide with each other. As the energy is converted into heat the molecules slow down. There is a theory that when the molecules stop moving there will be no heat. That is the point known as absolute zero and has been given a comparative temperature of -273·15°C.
Unless energy in some form is applied all atoms or molecules they will stop moving.
Tracy and Roger could bond a foam insulation that has a reflective plastic foil behind a bonded layer of plasterboard. The sheet material would be bonded to the concrete walls with adhesive. There are various thicknesses of the thermal lamination that will reduce the speed that the heat will be lost in the wall.
60mm of foam insulation plus the reflective plastic foil layer covered with 12.5mm of plasterboard will make a difference. It is not cost effective but it will make a noticeable and measureable difference to heating the apartment.
Problems include water vapour going through the gaps in the insulation. The foil layer is not continuous. Does it matter? In reality probably not. Technically it ‘could’ enable the water vapour to condense behind the thermal board and lead to debonding or blowing of the adhesive.
The other issues are the electrical switches and sockets would require re-wiring so that the cables are long enough to allow for the thicker wall. The joints around each switch technically could allow vapour to pass through.
The window returns known as the ‘reveals’ will be difficult to insulate especially if the windows have recently been replaced. Window boards will need to be higher and the soffit (the top part over the window) will be much lower due to the insulation. Yes very costly and compared with the saving in energy use it is not economical.
Ensure the electric radiators are the efficient types. There are wall panels that are relatively low Wattage and used for ‘background heating. They are ideal for leaving on all of the while to keep the apartment from getting very cold. That will also help with the condensation situation as the ‘fabric’ (term used to describe all the materials used to form the building) will remain warmer albeit only slightly warmer.
When the apartment is occupied additional heaters would be used. There are mobile ones that have a maximum heat output of 3kW. Dimplex make a Cadiz oil free radiator that will cost about 45p per hour at maximum however the thermostat will turn the heating elements down or off when the room heat is as required.
The other significant energy saver is thick heavyweight curtains ideally with a thermal lining.
A heavy weight curtain that is placed on the window board will significantly reduce the heat going out the windows at night. If there is a radiator on the wall below the window the warm air will be deflected away from the window as opposed to up and behind the curtain.
Having a thermal lining traps a layer of still air behind the curtain further reducing heat loss. Note reduces – nothing can stop it. Putting the curtain up on the window board may not look pretty but the difference in thermal comfort is considerable and at no extra cost.
Window blinds are not as effective as thermal barriers. There are thermal vertical slatted blinds that are good at reducing solar gain and reduce heat loss but they are not as efficient as heavyweight curtain material.
Without going too technical there is air resistance that has an effect. A soft rough surface will slow the air movement. In contrast a hard smooth surface will have little resistance so the air moves more freely.
Nothing in this blog is revolutionary. It is all basic science so why did the architects and designers get it so wrong? The concept of high rise is not a problem. The design and choice of the structure is though.
That is the subject of next week’s blog; heat transfer.