Heating News – December 2018 – Zombie Apocalypse Edition

Heating News December 2018

Zombie Apocalypse edition.

We’ve covered the heating of old farmhouses so much already that if you are not in a house that is warm, cosy and cheap to run then you haven’t been paying attention. What about the Zombie Apocalypse though? If there is a power cut, all heat pumps, gas and oil boilers and most PV systems don’t work so a wood burner will be handy when the grid gets hacked, whether by Zombies, Russians or just bad weather. Connected to a heat bank that wood burner will provide heat, cooking, functioning radiators so not just a nice thing to have but maybe even a life saver.

But enough about that. Not everyone has a leaky old house with a siphon attached to their wallet. The other end of the spectrum – a Passivhaus – is pretty astonishing with heat losses so low that just by turning on the lights, TV and computer would pretty much cover the heating needs.

 

insulation matters

This diagram shows how energy demand falls as insulation values rise. The Passivhaus demands are so low that heating is hardly needed. It’s not just running costs that are trivialised. The actual build costs are reduced because there is no need for under-floor heating and no powerful heat sources to drive it. Usually a small heat pump using no more power than an electric kettle will be more than adequate.  This is offset by the cost of extra insulation but the savings are there forever and the Government RHI will pay for the heat pump too.

So what is a Passivhaus?

It’s all about insulation and airtightness. Insulation of walls floor and roof have to be slightly better than current UK regs, but not by that much, and the building must be a bit more airtight than usual but again not by that much. Heat loss is measured by U values (which we’ll examine below) and airtightness is measured in air changes per hour. Basically a fan blows up the pressure to 50Pa for a maximum of 0.6 air changes per hour and then the same again but with a negative pressure. A Pascal is the pressure of one Newton/sq metre so a bit like a minced apple spread across your desk.  50Pa is very low so with careful building and lots of tape the standard is achievable. Sealed doors and windows will close with more of a ‘schmwuk’ noise than a clunk and the house will probably feature triple glazed windows and mechanical ventilation with heat recovery MVHR. Passivhaus gradings relate to how much renewable energy they give back so for the top tier ‘Super’ the roof will be heavily covered by solar panels to make 120kW/m2/annum (footprint). The overall target U value for a Passivhaus is 0.15W/m2K so lets see how that compares with traditional practices.

U-Values

This value relates to the ability to flow heat energy across a surface so it is measured in Watts per square metre and takes into account the temperature difference across the surface, so W/m2K. So a Passivhaus with an external shell of 800m2 and U=0.15 would need 1.2kW when the outside temperature is 10 degrees colder. This ties closely to the Passivhaus limit of 15kW.hr/m2/annum (on the footprint) for total energy consumption.

Traditional practice U values  W/m2.K

Brick wall                          2

Cavity wall                        1.5      Note: this is 10 times worse than the example above

Insulated cavity wall      0.18

Concrete                             1.5

Single glazed                    4.8 – 5.8

Double glazed                  1.2 – 3.7

Triple glazed                     < 1

Wooden door                    3

Note that some popular modern building methods are not really up to scratch and need extra insulation to get towards Passivhaus. Eg Durisol insulated concrete forms 0.15    Structurally insulated panels 0.14. Adding extra layers of insulation is needed and to get the final U value you add the reciprocals of the U values of the layers then take the reciprocal of that for the final figure.

Current SAP rules

Wall      0.18

Floor   0.13

Roof    0.13

Glass   1.4

No doubt you have noted that glass is a five lane highway for heat loss especially on the North side of the house. South facing glass is different because it behaves just like a solar panel and gives back much more than it loses. For example the daily solar insolation average in Kw.hrs per square metre (Brighton) is: Nov 1.7, Dec 1.14, Jan 1.43, Feb 2.17. The obvious conclusion is that lots of south facing glass is often good enough to heat the house especially if accompanied with high thermal mass floors/walls and covered at night with shutters and curtains.

Now we have a house that barely needs heating and sells power to the grid but there will be days when some heat is required. The bills here are going to be so low that the choice matters less, but for a small house I’d go for a low powered heat pump because:

Heat pump power

The RHI payments are good, it’s ecologically sound, it runs on similar power to an electric kettle and the PV panels will run it free on most days.  Air conditioning can be incorporated when partnered with fan-coil units. N.B. There is no RHI for aircon enabled heat pumps so a separate chiller unit would be required.

What about a wood burner? – well of course, we love them and there is the Zombie Apocalypse looming.

DIY fan-coil unit

DIY fan-coil unit

No underfloor heating, no radiators, it has to be fan-coil units. There is a full description of the Original Twist version here.

It’s a cheap and easy DIY project.

 

1st year with Google Home and Chromecast

Verdict: So good we have 3. Main uses, TV control, intercom, encyclopedia, alarm.

Radio? They’re obsolete

Remember when a DAB radio with preset buttons was a Christmas present favourite? Well those days, in a flash, have gone. A Google Home will tune in practically any radio station; all you have to do is ask. Turn up the volume? “Hey Google, turn up the volume”  “Hey Google set an alarm” So it’s a radio but, of course, so much more with your Spotify playlists to hand, and via Chromecast, control of the TV, Netflix, YouTube … etc … but you know all that. It’s just fascinating how as an almost inconsequential aside this device has consigned an ubiquitous bit of kit to history. Will the next generations even know what a radio is.

That’s all for now. If you need advice, a stove or a heatbank in UK, France or Italy please contact me on the form below.

Advertisements

DIY fan-coil heater

DIY fan-coil unit

Fan-coil unit

You might be surprised to know that if your house build is anywhere near Passivhaus standards then minimal heat demand makes underfloor heating a waste of time and money. Well, that’s a big saving so bring it on but what to do instead?

Underfloor heating did away with horrible radiators, and we don’t want them back, so that just leaves warm air blowers such as kickplate heaters – i.e. water powered puffer heaters.

On the walls without plaster theme here I proposed a kickplate heater, in the lower cupboard part, to give an occasional guff of hot air and for slightly under £200 you can do just that. However these neat little units aren’t perfect. They have to shift a lot of air through a small aperture so they are intrinsically noisy, draughty and the heat exchanger, or a filter, can clog with dust and pet hair fairly quickly. Larger versions are available but they aren’t so neat and they are much more expensive.

So here’s the Original Twist alternative which is cheaper, quieter and more reliable.

Lets assume that the low cupboard bit of your wall is made of typical 720mm x 300mm kitchen carcass units. A pair of them 600mm wide with a large slot cut out of the inner sides allows a 1000mm x 500mm x 70mm double radiator to fit inside (£48.14 Screwfix). Each of the top shelves is fitted just low enough to mount a 140mm fan from a computer (£10 – 20 Amazon etc) and these gently blow air past the radiator and out of the bottom. You can decide where the air inlet goes: probably top front but a wall panel channeling much warmer air from ceiling height is worth a thought. This unit also does air conditioning when paired with a suitable heat pump so a length of plastic guttering under the radiator will catch any condensation.

You might want to kill airborne pathogens. There is plenty of space in the box for a pair of UV lamps but if you do fit them then avoid PEX water pipes because UV will kill them too. Fitting UV tubes in the top sections with the fans underneath is probably the way to go.

Controls:  The fans are switched on automatically when either hot or chilled water arrives at the radiator. An ESCO solar controller does all that for £45.50 or about half that with a frost stat and a 2 pole thermostat. You’ll also need a variable resistor for speed control. The fans are 12v so you’ll need a power supply and, like the fans, these are cheap PC components. Remember that the LED strip lights in your integrated beam floor could be 12V and might like to share that power supply.

And that’s it really. A few simple components all easily obtained and making the perfect, reliable fan-coil unit. When turned down to essentially silent the fan pair will move about 100cfm and the heat output will be between 1 and 2kW depending on the water supply temperature.

You might wonder why all this effort gives you anything better than the radiator fitted as normal. The answer is that heat pumps don’t work efficiently at the 60c normally used with radiators. While under-floor heating is the best at low temperatures a fan-coil unit works reasonably well at 40c. The only reason our unit has a radiator is that with all the fins in a double radiator you get a high surface area for not much money. The heat delivery couldn’t be more different. A radiator wafts hot air straight up to the ceiling where it tends to remain – with replacement  air moving across the floor as a cold draught. A fan-coil on the other hand, blows warm air across the floor where it mixes with cooler air in the room and gives a faster and more comfortable heating experience.

insulation matters

Have a look at this chart on heating costs for various house types to appreciate why a Passivhaus with a small heat pump and some fan-coil units could be the way to go. You’ll see that the ASHP can meet the Passivhaus demand for almost no cost. Indeed if the ASHP is connected to PV panels then the running cost of the house will be close to zero.

I guess you might be in a state of shock now. Thousands saved on your heating strategy and air-conditioning a simple addition.

For more shocks and sleepless nights check out more building ideas on LIST OF POSTS.