MikeG.":zxye0qh6 said:
jimmy_s":zxye0qh6 said:
......The SCOP of the newer air source heat pumps are a lot better than they used to be.......
Claimed figures and actual in-use figures are very much like claimed MPG figures for cars. Real life COP figures of 2 are rare. When you realise that electricity is typically generated with an efficiency in the low 30% range, and with losses in the distribution the energy efficiency of the electrickery which actually arrives in your house is typically in the 25% to 30% range. It doesn't take a second on the back of an envelope to work out that in energy terms you would be way better off burning the oil or gas directly in your house in a modern efficient condensing boiler (efficiency, depending on how it is calculated, of 80%+........with claimed 95% + being worth another pinch of salt) than you would going the circuitous and inefficient route of burning it in a power station, converting that heat to steam to generate electricity to send miles down the wires where it is converted back into heat.
Of course, if all our power came from renewables, and there was capacity in the distribution system, then heating by electricity would be fine, despite its enormous inefficiencies. It doesn't, so it isn't.
here in the states (comment withstanding again about particulates), california is going so far as to get nat gas appliances out of circulation (dryers, cooktops/ovens, etc) for a simple reason - they're trying to control emissions of unburned gas and get everyone on grid as generation changes.
When you talk about something like oil instead of natural gas-generated electricity, you have to include the fact that there's quite a lot of energy spent in faffing about with the oil (probably so than there would be if you were burning gasoline in a car). And there's a quite a bit of filth released burning oil compared to natural gas.
What the energy company does to generate a converted BTU of electricity will be at far less cost than you burning oil, and the idea that you're burning a btu and 0.95 of it goes into your living space is a bit funny (and if it does exist, it erodes as the equipment gets old).
We burn gas here for heat. I pay about double the amount that the power generation company does. If I burned oil, i'd be done burning oil at this point and go to a geothermal system for one simple reason. a 100% efficient electrical coil probably has about 3.5 EER. with an ambient outdoor temperature of 45 degrees F (probably about 8C), the system uses one kilowatt to generate 21,500 btu of heat. You can pencil that out. It's probably more efficient to exchange heat with the outside air (which is where most of the heat is coming from) than it is to burn fuel and transfer the heat from the burning through your system.
The case where I'm not peeing into the breeze here with natural gas is that it gets much colder here than there. below 0F at night several times a year. The only thing that makes that swing efficiency wise is geothermal, where you get the favorable equivalent of the heat exchange mentioned above all the time because the exchange is going on with the ground. The trouble is, a 5k heat pump install (if you had such a thing air to air) becomes about 15k here in the states and it doesn't pencil out yet with nat gas. It does with oil (keeping in mind that we will spend more btus per square foot because our average fall and winter temperature will be lower than probably anything in the UK, and definitely lower than much of it).
The overall EER rating (vs. seer) of my 21 SEER system is about 14 or 15 (I don't remember exactly, but it's one of those). If we hit that target on the heat side, we're still as efficient or more efficient than your oil burner 14*0.25 vs. 3.5*0.9 or so). With less particulate in the air by a long shot.
