Oh dear.
Z.
Heat pumps have their merits but some users or potential users have unreasonable expectations.
Firstly, the heat is not free or even nearly free, as some expect. The electricity consumption is significant and must be allowed for in terms of both paying the bill and in sufficiency of supply.
Secondly, a heat pump must be correctly specified according to the heating demand, and then correctly installed.
Too many heat umps are undersized in relation to the heating demand. Other are connected to existing radiators which is unlikely to work well.
Sounds like the consumer didn't appreciate the thermal inertia of the building either. My parent's old cottage would take many days to heat up if they ever let it get stone cold in winter (even using and oil boiler & radiators) - just due to the vast amount of stone (and clay) in its old thick walls. If you add good thermal insulation on outside of the walls you reduce the heat loss, but the heat needed to raise the temperature of the walls themselves will still be the same. Make the new heating system much smaller to match the now reduced heat loss (as is usual, as it's cheaper that way) and heat up times will naturally be extended. Typically not a problem of course, if the house is kept warm in the first place (as most homes are).
- Andy.
Do people keep the heating on all the time nowadays even when the house is empty?
Most modern (programmable) thermostats don't so much switch on and off, as change the target temperature - lower when unoccupied, higher when occupied - the choice of the ‘setback’ temperature being influenced by typical warm-up times. Some smarter ones can even learn the room's typical response to heating and adjust the actual setback temperature and/or anticipate a programmed change to a higher temperature so the room reaches the required temperature by the required time.
A slightly different mind-set is needed when dealing with small heating systems in well insulated but high thermal capacity buildings, as compared with the large capacity heating systems in old leaky buildings we're perhaps more used to. It may well be more economic to keep the heating system running for a week or two when away (losing only a small amount of heat due to the good insulation) than let the building gradually get cold and then heat it up quickly again on return - as the latter approach would require a larger heating system which likely would not only cost more to install but run less efficiently during the rest of the year.
Good levels of insulation (and airtighness and controlled ventilation) can make huge difference to heating demand - e.g. a typical 1970s house might have a space heating requirement of something like 150kWh per sq m per year - nowadays we can achieve something closer to one tenth of that - around 15kWh/m2/y - at those sort of differences the savings from turning the heating off for a couple of weeks, only to have to re-heat the structure, really can be quite small.
- Andy.
The biggest design problem is the way that people think they can just replace the gas boiler and get any reasonable efficiency. The coefficient of performance (COP) of a heat pump is directly related to the temperature difference across the pump, in the same way as water and a water pump. More head takes more power in pretty much direct relation as more work is done. If the temperature difference is small the COP can be quite large, perhaps as much as 10 for a fridge on a cold day in the kitchen, but the freezer in the same conditions will get 3-4. Air exchange heat pumps have another problem when the temperature is somewhere close to zero, and that is that the evaporator (the outdoor bit gaining heat) may well freeze up with ice and block ait flow, just like the fridge but worse because of the high air flow.
It is being suggested that radiators may be used with water at 50-60C. This is mad as we only need to heat the air to 20C, so why not heat it directly which will give a much better COP as the condenser temperature needs to be little more than 20C to work. Such systems are in common use in offices and commercial premises. Thus we exchange a temperature difference of 60C for 30C and the COP will approximately double. Surely these “fine minds” planning the Green revolution know just a little science?
Actually, I am sure they know none whatsoever, and if they did this Climate and Green nonsense would have stopped dead in its tracks. Clearly, the IET editorial team does not either, as the latest E&T shows, it is simply regurgitated press releases from the COP26 mob. Why an Engineering Institution has so little science and engineering knowledge is completely beyond me. The most interesting point is that they don't want to listen and learn either!
davezawadi (David Stone):
It is being suggested that radiators may be used with water at 50-60C. This is mad as we only need to heat the air to 20C, so why not heat it directly which will give a much better COP as the condenser temperature needs to be little more than 20C to work.
Because if you have a 100+ year old building as I do, with 20+ radiating radiators (the old rib-type, not the newer thinner ones with cladding) then 50°-60° is the temperature you need to get them to radiate warmth into the room effectively. My pipes also run free inside the room, so I get a bit from that also.
Also, all the thermal energy imparted to the heating water starts inside and stays inside the building throughout its life, so it is not as if any thermal energy is being lost that way.
Such systems are in common use in offices and commercial premises. Thus we exchange a temperature difference of 60C for 30C and the COP will approximately double. Surely these “fine minds” planning the Green revolution know just a little science?
Yes. Let's see, I could insulate my building, exchange all the radiators for air-convection heating and live happily ever after ….. except for the €250,000 it would cost me to do all that and the hefty monthly repayment on the loan.
However, your observations do resonate with something I had been thinking of doing. Keeping the building at, say, 14° with the radiators, and installing air spot-heaters in each room, run from a PV installation + battery, that turn on when the room is occupied. Practically, I know it works because I have tried it (a really annoying trial, though, because I only have one spot heater, a Dyson - they are not inexpensive - and had to cart it around with me/us. I also used 16° as the basis heat). The other practical issue is that there are no DC spot heaters on the market, so “direct drive” is not currently possible.
I am in a different climate, though. We do go down to -15° or lower for a day, or a week, or a couple of weeks, as we did this February.
Actually, I am sure they know none whatsoever, and if they did this Climate and Green nonsense would have stopped dead in its tracks. Clearly, the IET editorial team does not either, as the latest E&T shows, it is simply regurgitated press releases from the COP26 mob. Why an Engineering Institution has so little science and engineering knowledge is completely beyond me. The most interesting point is that they don't want to listen and learn either!
I have plenty of science and engineering knowledge (although by no means as much as some). If you don't get the worry about global warming, I could introduce you to my Californian pals who are worried about the state burning up regularly and that large swathes of it may be rendered unliveable within a couple of decades. Or to my German colleagues trying to clean up after the more-than-thousand-year floods, not to speak of those mourning for friends and relatives they lost. I can also give you a reading list that would make the issues clear. Please ask.
Hi Peter
I do not wish to upset you but your comments do not make thermodynamic sense. I would also disagree with you about the science in a fairly spectacular way. However, you can easily check for yourself. NASA publishes the figures from its satellite temperature probe and you will see from these that the Earth overall has cooled for the last 6.5 years at least. If the CO2 hypothesis were anywhere near correct or useful it would not work because it predicts a temperature rise entirely based on CO2 levels which have increased linearly over the period. Another clue is the Muna Loa CO2 figures which show a linear rate even though during the Covid the fossil fuel use has reduced by about 30% Worldwide. This should show as a change in the CO2 graph, which it does not. Would you like to explain these anomalies in your thesis?
davezawadi (David Stone):
I do not wish to upset you but your comments do not make thermodynamic sense.
This is not very informative. I presume you are talking about what I wrote about my building. Can you say where you think they are wrong?
I would also disagree with you about the science in a fairly spectacular way. However, you can easily check for yourself.
Thank you for the tip.
NASA publishes the figures from its satellite temperature probe and you will see from these that the Earth overall has cooled for the last 6.5 years at least
Oh, dear, here we go again. Roll out the tropes. I wonder what order they are going to come in this time?
“The earth overall has cooled” is a pretty vague statement and as it is does not make much sense. “The Earth” radiates out what it receives from the sun. There is a general equilibrium. What most people are concerned about is tropospheric, actually biospheric, warming. This is accompanied by stratospheric cooling. Roughly how much was first shown, I think, by a gentleman named Manabe, who just won the Physics Nobel.
If the CO2 hypothesis were anywhere near correct or useful it would not work because it predicts a temperature rise entirely based on CO2 levels which have increased linearly over the period.
That C02 emissions lead to tropospheric temperature rise is not appropriately called a “hypothesis”. It was explained in the 19th century. The Nobel prize proclamation for 2021 said that Klaus Hasselmann's fingerprinting technique has “been used to prove that the increased temperature in the atmosphere is due to human emissions of carbon dioxide.” Note that word “prove”. Are you as good as that?
Another clue is the Muna Loa CO2 figures which show a linear rate even though during the Covid the fossil fuel use has reduced by about 30% Worldwide. This should show as a change in the CO2 graph, which it does not.
The fact that you think somewhat reduced CO2 emissions in one year (normally it takes years to estimate emissions since the data takes a while to assimilate) should lead to reductions in Keeling's series in the same year tells me quite a lot about what you know about climate science. :-(
Would you like to explain these anomalies in your thesis?
They are not anomalies to people who understand some basic climate science. “Misunderstandings” would be a more appropriate term.
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