PBut they are less than this, they average around 30 degrees for the warmest spot on the radiator, usually taken as top middle rear panel, the bottoms of the panels and often the front panel are cooler, so the actual average temp is even less.

 

     

I'd always heard that if rads were warm on top and cool on the bottom then it was a flow problem (too low) and the other way round was usually air.  Echoing what @batalto said; my flow rate is about twice what yours is and my heat requirements are a bit less.  

Hi @cathoderay

I am pleased to see that the temperatures within your home are increasing, though it is undoubtedly due to the warmer weather.

I don't think that I explained things clearly yesterday, and it does take some time to get ones head around the different aspects at play.

Energy, to quote from Wikipedia is 'the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it'.

Power is 'the amount of energy transferred or converted per unit time'.

The SI unit of measurement for energy is the Joule and for power is the Watt, though they are both inter-related in that the Joule is sometimes referred to as the Watt-Second. 1 Joule is equal to 1 Amp flowing through a resistance of 1 Ohm for a period of 1 second, which is equal to 1 Watt-Second, therefore 1kWh is equivalent to 3600000 Joules or 3.6MJ.

I must admit I sometimes have difficulty whether to use the term power or energy, but I think the easiest way is to say that energy is kW and power is kWh. So, when I boil the kettle to make a cup of coffee, I am using 3kW of energy, but only approximately 50Wh of power.

What we often refer to as heat, is the transfer of energy from one body to another thermodynamically, which is why I often use the term heat energy to differentiate it from electrical energy.

With regard to the flow measurement displayed on your controller, it very much depends upon how the flow rate is being measured and presented. I doubt that it will be an instantaneous value, so will probably be averaged or integrated over a period of time. The water pump inside the heat pump unit may also continue to run even after the compressor has stopped so that correct water temperature measurements are being made.

With regard to the temperature measurements on your radiators, it is very much dependent upon where you are taking the measurement in relation to how the water is flowing through the radiator. If the water is entering the radiator at 40C and exiting the radiator at 30C, then dependent upon where you measure the temperature you should get a reading between 30C and 40C. This is why I suggested measuring the the inlet pipe and the outlet pipe, the average of the two readings will probably give a more accurate representation of the effective radiator temperature. In the area where the water is entering the radiator it will achieve a higher metal temperature and therefore emit more heat energy into the surrounding air. As the water cools as it flows through the radiator, the amount of heat energy being emitted reduces. The total amount of heat energy being emitted by the radiator is therefore dependent upon the temperature of the water entering, but also the flow rate which denotes the amount of heat energy being supplied.

As Kev has suggested, you appear to have a flow rate problem, so I would suggest that you check around your system to ensure that you do not have any partially closed valves or filters that may be blocked.

Also carry out the suggested water pump and TRV tests. A further item to consider is the size and type of your diverter valve, which may be causing a restriction to the flow.

@derek-m Good point and one that should be followed with mass flow rate for heat. The water temperature might be 50 degrees but if the flow is low you just cant move that heat as you don't have the capacity to carry much heat. If you cant carry much heat, you cant transfer much heat. If there is a mismatch between pump flows and heat transfer into the house the water in the rads will be cold as it just wont get warm because there wont be any heat to transfer in.

@kev-m The graphs are from the OpenEnergyMonitor emoncms add-on app called "MMSPHeatPump" which was posted to their forums. The output from the default app "My Heatpump" shows only some of the info, but all on one graph.

@batalto (and others) - having cleaned the filter, and let the system run for a while, I am pleased to say the Midea controller is reporting a higher flow rate, 1.39M3/H, considerably higher than it was before cleaning (0.83M3/H). More importantly, the rads and rooms are warmer:

Bedroom 20 (vs 19), bathroom 21.0 (vs 22), kitchen 19.4 (vs 19); bedroom rad 20 (ie its at room temp, still stubbornly not warming up), bathroom rad 36, kitchen rad 34. But then again. its 12 degrees ambient outside, so everything should be up to heat!

@derek-m - when I do a one off rad temp measurement, I take the reading from the warmest to the touch part of the rad, usually top centre of rear panel.   

It seems crazy to have a four figure sum heat pump at the mercy of a very crude throttling filter bang in the way of main flow. Also, no alert/error appeared on the controller, even through there was an apparent notable reduction in flow. If we can put a man on the moon etc etc surely we can come up with a better filter design and better monitoring. As things are, I will check it again in about a week.

The above suggests restricted flow may have been a problem, but on the primary circuit, rather than the secondary circuit. In the spirit of changing only one thing at a time, I think maybe best to run it for a few days, and see how things work out. The problem is as we move into spring and then summer there are going to be less and then no opportunities to observe the system in cold conditions. When things are cold, I suspect I may also have symptoms suggestive of a flow problem on the secondary circuit. 

Posted by: @derek-m

I must admit I sometimes have difficulty whether to use the term power or energy, but I think the easiest way is to say that energy is kW and power is kWh. So, when I boil the kettle to make a cup of coffee, I am using 3kW of energy, but only approximately 50Wh of power.

Thanks very much for the further info, and thanks @batalto for highlighting how flow affects things. I'm sort of getting my head round the whole business. But I can't help wondering if in the quote above you are checking whether I am paying attention! Aren't energy and power and/or the units the wrong way round? Or have I completely lost the plot?

@cathoderay your system is now carrying more heat into the exchanger. If you imagine 1390 litres of water (1m3) at 50 degrees that contains more energy than 830 litres of water at 50 degrees.

830 litres from 30 to 50° is 19.3kW

1390 litres from 30 to 50° is 32.3kW

You now have over 10 extra kW of heat to transfer into your house.

Also on the flow, you can't have been far from the low flow error I experienced. Looking at your temps I don't think your radiators are balanced. They should all roughly be the same temperature.

On the point above think of things like buckets. The kW power is a bucket that can hold 3kW of power, kWh is like flow rate from that bucket. Over an hour 3kw can leave the bucket. If you only run it for 30mins your 3kw bucket will supply 1.5kwh of power. This is why your 3kw kettle only uses 50watts. It doesn't run long enough. If you kept it running for an hour it would use 3 kilowatts of power. Does that make sense?

Bear with me on this…. Most base things we measure are quantities, not rates… Miles, kg, apples, bananas.  The rate for miles is then in miles per hour.  Energy is unusual in that the unit we generally use is based on that of power, the Watt or kW (1000Watt), and energy is then in kWh, that is kWatts times number of hours.  It frequently causes confusion, and often kW/h appears, intended to be the rate of energy, I guess it’s similar to miles/hour, which we’re comfortable with!  Just to be clear, kW/h is almost always wrong.

So kW is a power.    Its the rate of using energy.  A car engine has a power rating, the fuel tank or battery can store a certain amount of energy.  A kettle will be 3kW power rating maybe, and if it’s on for 6 mins will use 0.3kWh of energy.

A kWh is a unit of energy.  We may often measure things like how many kWh a fridge uses in a year (it’s written on the label these days).  It’s odd really, that example is in kWh/year which is a power again, strictly. 

kW and kWh are used wrong or interchanged so often these days, even in newspapers and published material.  Power, Energy, Heat too.  (Heat in engineering speak is thermal energy in kWh).

@robl

I would suggest that you all look at Wikipedia.

@cathoderay looking this morning my flow rate was is 1.41m3/h so close to yours - but this was for hot water. Got heating right now it's 1.78m3/h

Posted by: @derek-m

...

I don't think that I explained things clearly yesterday, and it does take some time to get ones head around the different aspects at play.

And I'm still struggling.

Energy, to quote from Wikipedia is 'the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it'.

Power is 'the amount of energy transferred or converted per unit time'.

The SI unit of measurement for energy is the Joule and for power is the Watt, though they are both inter-related in that the Joule is sometimes referred to as the Watt-Second. 1 Joule is equal to 1 Amp flowing through a resistance of 1 Ohm for a period of 1 second, which is equal to 1 Watt-Second, therefore 1kWh is equivalent to 3600000 Joules or 3.6MJ.

...

 I get that the basic energy unit is the Joule, and that a Watt is one Joule per second. I also get that a flow of 1 Joule per second over 3 seconds will deliver the same number of Joules (i.e. the same total energy) as a flow of 3 Joules per second over a time period of just one second.

I'm also happy with the idea that 1kWh is maintaining a flow of 1kW (i.e. 1000 Joules per second) for 1 hour or, of course, 2kW for 30 minutes and so on. That fits in with your explanation, @Derek-m, that eventually all it's doing is delivering a total amount of energy (3.6MJ), and that the numbers only dictate how quickly or slowly that total energy is delivered.

What I struggle with, however, is that it looks to me like both kW and kWh are units of power i.e. dependent on time. It's the fact one is per second and one is per second every second for an hour that gives me headaches when I try putting them into practice.

As @robl has pointed out, it is easy to get confused by the apparent similarity between mph (miles per hour) and kWh (kilowatt hours) but there is the crucial difference he points out: with mph it is miles per hour (divided by: 120 miles travelled over 2 hours = 120/2 = 60 mph) whereas with kWh it is kW times hours (multiplication 2kW convector heater on for 2 hours = 2 x 2 = 4kWh). One is a rate, the other in effect a quantity, in this case of energy.

Nor are things helped I suspect by the fact the definition of a Watt, which is itself a rate: 1 joule per second, where joule is a unit of energy. So a watt is a measure of the rate of energy transfer. So we continue to have the time floating around, in the case of a watt it is one joule per second, in the case of kWh, it is kW for so many hours. 

@derek-m - I gave up on wikipedia on its article on watts in the first sentence, when it mentioned radiant flux. It suggested an author who had God on his or her mind. I tend to find on scientific matters wikipedia tends to jump too quickly into baffling equations, and the article on watts is no exception. When they are not getting religion, wikipedia authors all to often come across as trying to showcase their apparent knowledge of the esoteric. It usually just leaves me baffled. As I mentioned before, I understand things best by working with principles and concepts, from which the maths naturally falls into place.

Which leaves me with this as my current working understanding of power and energy, as applied to central heating:

Power in kilowatts is the rate of energy transfer/loss, the rate at which energy is going from A to B. It might be rad to room, or house to environment, or boiler to circulating water. Power is the right word, the wattage of something tells us how powerful something is. A 3kW fan heater is more powerful than a 2kW heater, a 16kW ASHP is more powerful than a 14kW ASHP (until you flip the dip switches...).

Energy in kWh is the amount, or quantity, of energy consumed. The more powerful something is (in kW), the faster energy gets used, and the longer we run something, the more emergy we use, so to get total energy use we need to know the rate of energy use (how fast we are using it) in kW, and how long we used if for, so we multiply by hours. A 2kW fan heater on for 2 hours uses energy at the rate of 2kW (remember one fundamental definition of power is joules per second, where joules are a measure of amount of energy) and it does it for 2 hours so it consumes 2 x 2 = 4kWh of energy. The same heater on for half an hour would consume energy at the same rate, but as it is only on for a quarter of the time, it will use on a quarter of the amount of energy: 2kW x 0.5 hours = 1kWh. The maths follows from the principles.

One way of remembering the difference is to ask, what do we mean when we say this fan heater is 2kW, and this one 3kW? We mean the second one is more powerful, so kilowatts are a measure of power.   

Where it gets complicated is in the rather sloppy usage. Sticking with kW = power = a rate, and kWh = energy = a quantity, it follows that when we talk about heat loss, it sounds as though we are talking about a quantity of something (we lose quantities of things, as in we lose a quantity of money), but, because of convention, we are in fact describing the rate of loss, not the absolute amount of energy lost. To find out the absolute quantity of energy lost, we need to multiply the rate but how long that rate has been running for. If my house has a 12.5kW (rate of) total heat loss/demand, that means in one hour my house my house will lose (and so demand, to stay at a steady temp) 12.5kWh of energy.

Likewise with rads and boilers (or heat pumps). A 2kW rad delivers energy at a rate (joules per second) of 2kW, if it is on for an hour it will consume a quantity, of 2kWh, of energy. A 14kW heat pump delivers energy at a rate (joules per second) of 14kW, and if it runs for an hour at this rate, it will consume 14kWh of energy.

The final piece of the jigsaw: how does this apply to circulating water? I think maybe the answer here is to consider that one litre of heated water contains a quantum, and so amount, of energy. It's an amount, not a rate, and the higher the temp, the greater the amount. For example, a 14kW heat pump transfers energy (as heat) to the water at a certain rate, and so the water contains a certain number of kWh (a quantity) of energy, the amount depending on the rate of transfer (how powerful the heat pump is) and how long the heat pump has been running for. A 14kW heat pump adds energy to the water (as heat) at twice the rate of a 7kW heat pump, so after any given interval of time, it will have transferred twice the amount of energy, as kWh. What then happens is the circulating pump mechanically moves that quantity of heat energy from A to B (heat pump to rads), where it then gets transferred from the rad to the room at a certain rate, which depends on radiator size and water temp, which is why we say a rad is a 2kW rad at delta t of 50 (at this delta t, this area of radiator will deliver energy at this rate). The key thing is we are not talking about the quantity of energy delivered, but the rate. We have absolutely no idea of the amount (quantity) of heat energy transferred (which is the counter-intuitive bit, at least for me), we only know the rate. To get the quantity, we need to multiply the rate, in kW, by the time, in hours, get get kWh.

That, I think, is the fundamental problem, at least for me. I think I am dealing in quantities (amounts) - my rad delivers such and such a quantity of heat - but in fact, I am always talking about rates - my rad is delivering heat/energy at this rate. Luckily or confusingly, depending on how you see it, the two are very intimately connected: the amount (quantity) is simply the rate multiplied by the time (duration).                 

If we apply the idea that a litre of heated water contains a quantum (amount) of energy, the amount depending on the temp, then at a given temp, it naturally follows that the faster the water flows, the faster the heat (energy) gets transferred, ie the rate of transfer goes up (and because the rate has gone up, the amount during any given time goes up: they are intimately connected). 

A final analogy, to show that we are usually (always?) talking about rates, not amounts. Imagine water loss from a leaky bath. Some baths leak more than others. My ancient bath leaks 10 litres/min, so to keep my bath full, I need to add water at 10 litres/min. Strictly speaking, I have no idea how much water I have consumed, to know that, I have to specify a time interval, say 1 hour, is which case I have consumed 600 litres (I could also call them litre hours, if I patched up my leaky bath so it only lost 5 litres/min, I would consume only 300 litre hours of water, and so on, over a day it would be 7200 litre hours etc etc). We do the same thing with our heating, only (ever) talking about rates. That's they key thing to remember, although I might think I am thinking in amounts, I am actually thinking in rates.   

Posted by: @batalto

looking this morning my flow rate was is 1.41m3/h so close to yours - but this was for hot water. Got heating right now it's 1.78m3/h

Yes, very similar, and also very similar heat pump capacity values. My readings are currently 1.40M3/H flow rate and capacity hovering around 6kW running heating. 

We now know quite a lot about the primary circuit, assuming the Midea monitoring is reasonably accurate, and let's give it the benefit of the doubt and say it is reasonable accurate. What I now need is a way of estimating the flow (cubic metres per hour) in the secondary circuit. I am not sure if this can be derived eg from temp drops ie secondary flow/return temps at the PHE and/or an estimate of the quantity (volume) of water in the system. Unfortunately, I don't think the Grundfos tech data has anything as simple as a max constant flow setting = so many litres/min, because presumably actual flows are dependent on circuit resistance, all the pump is doing is keeping the flow rate constant, but no way of knowing what that constant is.

@majordennisbloodnok - I see you have just posted a comment as well, but I need to post this one before it self destructs, will then consider them in the round.                     

@cathoderay as a note my Midea is the 12kw version, however I doubt it working very hard at these ambients.

You should be able to estimate flow rates using a bit of maths. You know the flow rate and temperature going into one side of the transfer, we can punt on efficiency and call it 90% for transfer of heat and you know the incoming temperature to the exchange and outgoing temperature.

We also know The specific heat capacity of water is 4,200 Joules per kilogram per degree Celsius (J/kg°C)

heat = mass flow * specific heat capacity * temperature difference

kW = kg/s * kJ/kg/°C * °C

kg/s = litres per second (as its water). We'll rearrange the equation

kg/s = kW / (specific heat capacity * temp difference)

Its been a while since I did any thermodynamics, can someone confirm my ramblings?