The Room by Room Heating Revolution
Efficient on-demand heating and the switch from gas to electricity
(Extracts from my talk at The National Self Build and Renovation Centre 9th October 2016)
Producing your own electricity is now easy with PV and great progress is being made with cost effective battery storage. Other methods of producing sustainable, low CO2, energy (nuclear, hydro, wind) will likely be delivered to your house in the form of electricity.
Modern electric in-floor heating has efficiencies that an embedded wet floor heating system in a slab will never have.
So isn’t it time that sentiment starts to shift away from gas for space heating, to electricity?
And we ditch the radiator?
This graphic shows how wall mounted radiators are really convectors and how this can lead to problems with comfort. The warmed air rises to the ceiling and travels to the far wall. As it cools it will fall to the floor and a convection current will start to build. This can lead to stuffy head/ cold feet syndrome.
If your feet and ankles are cold, you feel cold. What do you do if you’re feeling cold? Turn up the thermostat! What will more energy from the radiator do? Speed up the convection current. Not a very elegant situation I’m sure you agree.
Floor heating places warmth where you need it, under your feet. As the warmed floor becomes a radiant body it warms other surfaces in the room and the air in contact with, and gently passing over, these surfaces becomes warm. As the warmed floor becomes a radiant body it also limits heat loss from you, with the result you don’t ‘feel cold’. The physiology of feeling cold is all about rate of heat loss.
OK – so floor heating can be a good idea from the point of view of comfort – but does it always work well?
In designing a floor heating system one of the goals is responsiveness. You need to avoid the storage heater effect.
You want the system to bring the floor up to temperature quickly. You want the floor surface isolated form the sub floor through insulation and the heater placed on top of the insulation. Otherwise if there’s a considerable lag due to thermal mass, time and energy are wasted.
Similarly, if, for example, the sun comes out subjecting the space to solar gain when the floor is already at the correct temperature, thermal mass means the room will become overheated even if the heating is turned off. In practice you end up opening doors and windows and wasting the (expensive) heat.
You also want individual room control
By individual room control I mean you want to be able to control the heating on a room by room basis according to usage patterns.
In my house the bathroom is on at 6.15a.m., off by 7. Kitchen on at 6.30 off by 8.00, Home office on at 7.30 off by 6 pm, and so on.
Of course, if you get the ‘Responsive’ aspect of the installation right, and your day changes so you want to use a room ‘out of hours’, it’s easy to click the heat on in that room.
Zonable is not good enough as it means some rooms are heated when not needed as you can see in the slide.
There are other considerations of course.
- Scalable – how will your chosen system cope when you decide you need another extension?
- Simplicity, reliability – moving parts, pumps, water, valves, servicing costs, ease of installation, expected life
- Choice of fuel – cost and future-proof
- Build height – especially renovations
Let’s look at the type of modern electric floor heater that moves us on a giant step, compared with the orthodox gas central heating, zoned radiator of slab floor heating system.
You can see that it’s a world away from early experiments with electric floor heating with a heavy cable embedded in concrete – high thermal mass.
Here the element is just below the floor surface and is on top of insulation. Very low thermal mass – just the tiles and tile cement really.
Now compare what I’ve just shown with a typical hydronic system:
The performance advantages of the modern responsive electric floor heater can be seen in this 24 hour chart:
These images illustrate storage and on-demand heating patterns more clearly. We are comparing on-demand responsive floor heating to in slab floor heating (storage heater).
Included in the graphs are: Outside temperature, Room temperature, Floor temp and setpoint (desired temperature).
Let’s look at the set point, the yellow line. Room temperature, which is the brown line follows the yellow line closer than the in slab heating graph. On – demand heating follows the set point line fairly closely as it has much quicker response time, thus increasing comfort levels (you’re warm when you need warmth, and cool when you need to be cool) and reducing energy wastage.
In terms of energy usage – well, that depends on energy lost. The difference between the room temperature and the outside temperature defines the thermal gradient. On these charts it’s represented by the area between the blue line (outside temp) and the brown line. It’s easy to see that the gap is wider for longer on the slab heating example than for the responsive on-demand installation. This illustrates how energy usage is always more with slab heating. Thermal mass for heating is not a good idea for most domestic situations.
My lightbulb moments…
- Floor heating, not radiators
- Room by room control, not zone heating
- Responsive on demand heating, not slab heating
- Maintenance free heating, not boilers, valves, service contracts, water etc.
- Clean, renewable, possibly free, energy, not tied to fossil fuel
On-demand, responsive, electric floor heating and modern insulation make all this possible