Posted by: @jamespa

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Fancoils are simply fan assisted radiators.  The actual radiator bit is usually constructed a bit differently, you can add a bunch of computer fans to an existing radiator to get a very crude implementation of the same principle and at least one manufacturer does it exactly this way.  Radiators operate largely by natural convection (not radiation!) and this limits the rate at which heat can be transferred from radiator to air.  By forcing air over them more heat is transferred (just like the fan in your car, computer etc).

This is an extremely interesting idea, and the fitting of computer fans is well within my DIY capabilities. Being low voltage, they would be easy to set up. I also have the 'benefit' of being partially deaf, (it is a very double edged 'benefit', overall it does far more harm than good), which means I am relatively untroubled by background noise eg actual computer fans never bother me.

Presumably the fans don't need to run continuously, but rather only when a boost is needed, eg during a post setback recovery boost and/or cold weather. The former could be done using a timer, the latter using the OAT (as measured by the heat pump...). Again presumably, what will actually happen, all other things being equal, is I will initially get a bigger delta T over the rad, which in turn will cause the heat pump to work a bit harder to get the RWT back where it should be, the overall effect being more heat delivered to the room.      

Posted by: @cathoderay

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Posted by: @derek-m

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Could you please provide a copy of the data that was used to produce the chart above.

I've already done that, it's in the December data I posted yesterday. You will need to do the regression, using only non-setback days, but that's no bad thing, it will verify (or not) my calculations.   

That's not being very helpful can you not just provide the expected data that you used.

Posted by: @derek-m

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That's not being very helpful can you not just provide the expected data that you used.

Given your low confidence in and derision for my data, my calculations, my charting and my interpretations, I think it is best if I give you the raw data (as I have done) and you repeat the calculations yourself. It's a useful and well established process which I am sure you know all about called verification. 

Posted by: @cathoderay

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Posted by: @jamespa

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Fancoils are simply fan assisted radiators.  The actual radiator bit is usually constructed a bit differently, you can add a bunch of computer fans to an existing radiator to get a very crude implementation of the same principle and at least one manufacturer does it exactly this way.  Radiators operate largely by natural convection (not radiation!) and this limits the rate at which heat can be transferred from radiator to air.  By forcing air over them more heat is transferred (just like the fan in your car, computer etc).

This is an extremely interesting idea, and the fitting of computer fans is well within my DIY capabilities. Being low voltage, they would be easy to set up. I also have the 'benefit' of being partially deaf, (it is a very double edged 'benefit', overall it does far more harm than good), which means I am relatively untroubled by background noise eg actual computer fans never bother me.

Presumably the fans don't need to run continuously, but rather only when a boost is needed, eg during a post setback recovery boost and/or cold weather. The former could be done using a timer, the latter using the OAT (as measured by the heat pump...). Again presumably, what will actually happen, all other things being equal, is I will initially get a bigger delta T over the rad, which in turn will cause the heat pump to work a bit harder to get the RWT back where it should be, the overall effect being more heat delivered to the room.      

Its fairly easy to do, Ive done it on one radiator as a trial using off the shelf components only except for a couple of pieces of wood which I cut to size.  Unfortunately I don't have a way to quantify the effect, but its definitely significant, perhaps 20-30% at a fan speed which is audible, but below the general noise in my living room so doesnt disturb day to day activities.

90-100mm fans are a good fit to K2 radiators, you can get a pack of 5 for £25 and they can be daisy chained electrically. There are simple pwm controllers available off the shelf which will ramp the fan up according to the measured flow temp (so its only on when the CH is on), for any more complex control system you might have to do something with a pi or aduino.  Your assumption about deltaT is absolutely spot on.

Posted by: @scrchngwsl

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We can learn a few things about the right strategy here, for example, not to recover too aggressively. From 1: Rather than having a fixed setback of say 18 degC, and then bumping it straight back up to 21 degC for daytime, why not raise it in increments over a longer period? From 2: Why not have a negative setback when it's colder, and a positive setback when it's warmer? i.e. during the afternoon, at the highest outdoor temp, run your house a bit warmer. From 3: use PID control as well.

I think this is the natural future of heat pump controls: instead of maximising COP, they should minimise running kWh. And then you can get into minimising costs and/or CO2 beyond that, by looking at when electricity is cheapest/cleanest.

Absolutely so in principle.  Whether there is sufficient incentive for manufacturers to develop sophisticated but easy to use controls of this kind only time will tell.  Homely is a good start.

Posted by: @cathoderay

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Posted by: @derek-m

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That's not being very helpful can you not just provide the expected data that you used.

Given your low confidence in and derision for my data, my calculations, my charting and my interpretations, I think it is best if I give you the raw data (as I have done) and you repeat the calculations yourself. It's a useful and well established process which I am sure you know all about called verification. 

I was expecting that precise answer. Strange.

Posted by: @derek-m

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I was expecting that precise answer.

Well, that's all good then, it means you understand the effect you have on people.

But I still don't understand why you don't want to verify (or otherwise) the calculations yourself. I have given you the sitting ducks, all you need to do is get out your machine gun, and mow them down.

Perhaps I don't understand the effect I have on other people...

@derek-m and @cathoderay, the exchanges in this thread are becoming counterproductive. I want to remind everyone that the purpose of these forums is to foster positive and constructive discussions. While disagreements are natural, it's important that we handle them constructively. From this point forward, any negative or sarcastic comments that don't contribute positively to the discussion will be removed. Let's focus on maintaining a helpful and respectful environment for everyone. Thank you for understanding.

Posted by: @editor

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Thank you for understanding.

I do understand, and your thoughts are also very much in my mind.

I have tried to operate restraint, but in my defence, I do have to say that within hours of my return to the forum after the Christmas and New Year break, when I posted as far as I can see non-inflammatory posts, a certain other forum member first accused me of cooking the books, then repeatedly came out with implications I was thick, and finally (the last straw for my patience) came out with "You would appear to be quite good at producing charts using flawed data, and misinterpreting the results." That phrasing is inflammatory, and that is why the ensuing spat happened.

That said, and in fairness I suggest @derek-m can make one response should he wish to, I now will do my utmost to restrain myself. Nonetheless, the point about @derek-m verifying my calculations remains, it is just good practice. 

quick question on likely savings.

There have been many people over the past year, shocked and surprised at how quickly heat is lost from a hot water tank. In addition I’ve looked at the heat trace of our DHW cycle and noticed that with our coiled heat exchanger there is (or appears to be) a lot of energy being used towards the end of the cycle to raise the Flow Temperature with only a small DHW gain (perhaps only 5c)

So my question is how much energy be saved by truncating the DHW cycle? Do any of you data buffs have a view - without exacting data? 

My perception is that the higher the flow temp on the graph the more energy is being used and the narrower the deltaT becomes the less energy is being transferred into the hot water tank. A half hour cycle will raise DHW to 43c while a 50 minute cycle only achieves 48c. 

(I’m not seeing the graphs I’m trying to post on my iPad but I’ll post it anyway and try to post the graphs on edit.)

Posted by: @cathoderay

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Posted by: @derek-m

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I was expecting that precise answer.

Well, that's all good then, it means you understand the effect you have on people.

But I still don't understand why you don't want to verify (or otherwise) the calculations yourself. I have given you the sitting ducks, all you need to do is get out your machine gun, and mow them down.

Perhaps I don't understand the effect I have on other people...

Please explain how I can verify your results if I do not have a copy of them?

Posted by: @sunandair

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There have been many people over the past year, shocked and surprised at how quickly heat is lost from a hot water tank. In addition I’ve looked at the heat trace of our DHW cycle and noticed that with our coiled heat exchanger there is (or appears to be) a lot of energy being used towards the end of the cycle to raise the Flow Temperature with only a small DHW gain (perhaps only 5c)

Thats inevitable particularly if the coil is fairly small.  At this point delta T between flow and DHW temp is small so heat transfer is small.  I do have a crude model if it helps, what particularly are you wanting to know.  Best approaches are:

• reduce the target DHW tems |(without reducing the flow temp) so that flow to DHW is greater 
• increase the flow temp (perhaps towards the end of the cycle
• use a PHE + pump instead of a coil which can achieve lower difference between the two sides
• stir the DHW tank (stratification means that heating the bottom bit of the tank is particularly difficult)

It might also help the 'end game' if flow goes in at the bottom of the tank and return from the top, because of stratification, however this is  possibly disadvantageous at the start of the cycle, Im not sure what the 'standard practice' is!