SteamyTea

Makes a change from counting the number of windows.

4.2 [kJ.kg-1.K-1] x 400 [kg] x (52 - 8) [ΔT] *0.00027778 [kJ to kWh conversion] = 20.5 kWh 20.5 [kWh] / 5 [kW] = 4.1 hours Now that is the worse case, so probably get that down to 2 hours as DHW, generally, is of no use below 30°C and you will not be using all of it.

what size is your DHW cylinder?

Whoops, 0.00027778 (fat fingers on a small screen) Whoops again, autocorrect.

There is a bit of terminology to learn. Energy is measured in MJ (megajoule). A joule is the standard unit for energy and when converted to base units of kilograms, metres and seconds is very small. Why the M for 1,000,000 is added at the front. Now no one, apart from us nerdy scientists, use MJs, and domestic energy is metered and purchased in kWh. MJs can be multiplied by 0.0007778, or divided by 3600 to end up with kWh. The k just means 1000, W is watt and h is an hour, which is 3600 seconds. Power (W) is the rate that energy is used. You can think of this as your miles per gallon in your car, with energy being how many gallons are in the tank. If your car does 40 MPG at 60 MPH, and your tank has 8 gallons in it, you can drive 320 miles over 5 hours and 20 minutes. A unit of power is called a watt, which is actually a J/second. Again a small unit, so a k is added. A k is 1000. This gives the more normal kW for a power rating. Boilers, heat pumps and even wood burners all have a maximum kW rating i.e. 6 kW. Radiators, UFH and fan heaters also have a power rating. (This can get confused by some people talking old imperial units of BTU and BTU/h, but we went metric in ,'73, so tell them off) Where it starts to get confusing is a house will need a varying amount of thermal power to keep it at a steady internal temperature. This is caused by external temperatures rising and falling during the seasons and even during the day. This can be overcome in a number of ways. The easy way, and the way old heating systems were set up, was to fire up a boiler at full power, heat some water, pump it around the house to all the radiators, which then heated the air. When the house was up to temperature, the thermostat turned the boiler off. When the temperature dropped a few degrees, it turned the boiler back on. These days we are a bit more sophisticated and try to deliver enough energy to match the losses. This keeps the house at a steadier temperature, and used less energy overall. You will almost certainly read on hear about weather compensation (WC). This is just a basic feedback system that knows what the outside temperature is, how much power is being delivered to the house and for how long it may be needed. All that can be boiled down to a few numbers. The main numbers you need to know are the thermal losses for each room. Once those are added together, you get a number for the whole house. It is usual to size for a worse case i.e. -10°C outside. This gives you a maximum power requirement (heat source kW). Most of the time, you will be heating the house when it is way warmer outside, so the second number you need is about how much the heat source can be turned down internally. This is called modulation. Gas boilers have quite a high ratio, sometimes 10 to 1 i.e. 12 kW down to 1.2 kW. Heat pumps are not, generally, so good and are often in the range of 3 to 4 to 1. There are ways around this, but that is for later. The other thing that is important is domestic hot water (DHW). There are two ways to do this. Heat water only when it is needed (instantaneous), this requires a lot of power, often over 25 kW. Or Heat and store in a cylinder. This method takes longer for the same amount of delivered hot water, but used less power, often in the region of 3 to 6 kW. If the heat source is delivering both central heating and DHW, then this needs to be taken into account. With modern combination gas boilers, they are sized to deliver enough hot water, and rely on boiler modulation to deliver lower power for the space heating. Heat pumps, generally, rely on being only slightly oversized (which improves efficiency most if the time) and run a space heating time slot and a DHW timeslot at different temperatures and different times during the day. There is a lot of detail in heating design. So questions to ask are. Maximum house losses. Room by room heat losses. DHW reheat times.

Is it (expletive deleted)

I am sure mine does that, easily, since I put a RamAir sticker on the back.

That is a proper price. Gets the dirt off just the same as a £10k one.

I have no idea what that is, looks like an car.

FFS that system seems to be a disaster waiting to happen. Way to many stages and attention to detail, especially when you are up on a roof in a 30 MPH breeze, which is pretty normal down here.

Bit of a tricky one. At work, I often hear the therm 'I don't get paid enough to do this'. I pointed out the other day that if they were working at their peak performance, extra money could not make a difference. I feel the same about expensive items, which to me are generally add ons, not fundamentals. An example of this is car tyres. I can get a Goodyear for £170, or the ones I have, for £60. There may be a difference at the very extreme of performance, but as the ABS and stability control both work, I won't see the difference. I feel the same about a bathtub, or a kitchen work surface (I use a chopping board anyway). Maybe @Nickfromwales can join in as he often mentions the high spec places he works on.

I have seen the title term used, as well as similar terms like 'high end'. To me they just seem like marketing puff, and have no real meaning. If I was building a good house, it would have thicker walls, floor joists, stairs that bear onto a concrete floor. Basically things that give a very solid structure. What I would not consider is anything that is easily replaced, bathrooms, kitchens, doors and windows, which are nice to have, but do not really add real value in my eyes. A decent heating and ventilation system is important these days, but assuming the basic design is right, the replaceable heat source or MVHR unit is a bit of irrelevant as it can be changed. What do others think constitutes 'quality'?

I would hope so. (May have to check my figures as it seems wrong to me that they all have such similar volumetric expansions)

Was not argon filled anyway. I have always suspected that gases, even atomically large ones, get out over time though normal expansion and contraction. The volumetric thermal expansion of argon, oxygen, nitrogen and air, at STP, are all pretty similar at 3.4 x 10-3 K-1.

I have just remembered something from 40 years ago. I had a misted up DG unit that got cracked. The misting vanished. I wonder if a small drill hole in the edge (that pane separator bit) may cure the problem. May give it a go.