A friend of mine is having an Aira Heat pump installed and they have insisted on fitting a 4 port buffer tank. They will not guarantee the product without one.
They have also guaranteed a very good SCOP with their install.
The friend plans to install a level 3 emon HP monitor to verify their claims.
Where should the heat meter and pocket be installed?
My view is that they should be fitted on the flow and return of the secondary circuit, to and from the buffer tank and the house, as this will measure the heat energy actually reaching the radiators and tank.
Also the electricity monitor needs to pick up all energy usage including the secondary pump.
Has anyone got experience of monitoring a 4 port configuration?
Advice please.
Iâve got a 4-port âbufferâ (which I typically refer to as a Low-Loss Header) as part of my installation. (In my case thereâs no question it is required: I have 3 heating Emitter circuits, each with their own secondary pump, which need to operate independently. The LLH provides âhydraulic separationâ between those.)
Itâs important to measure all of the Heat coming out of the Heat Pump, no matter where that ends up, so (assuming thereâs only one Heat Meter) it needs to go on the âprimaryâ circuit.
Is the system also heating a Domestic Hot Water Tank? Hopefully the Buffer isnât part of that circuit - that would be A Bad Thing; where you wrote ââŚheat energy actually reaching the radiators and tankâ is that the DHW tank (or the Buffer tank)?
If youâre able to post a schematic sketch showing how you expect the components to be connected and where youâre proposing to locate the Heat Meter that would help others provide feedback.
(Thereâs a schematic of my installation in this post from last year: Help in diagnosing Nibe ASHP F2040-16 installation problems - #59 by dMb - these days I tend to refer to my installationâs 2-port Buffer as a âVolumiserâ instead, which I think is a less ambiguous term. Note my GSHP has separate Flow pipe connections for Heating and Hot Water, so I was forced to install two separate Heat Meters for those - but I just add the readings together.)
The heat meter should be fitted on the primary flow and return before the buffer since you want the monitoring to include losses from the buffer, also DHW wonât be going through the buffer.
Thanks for your thoughts and schematic.
You are right about the hot water tank the heat to that would not be captured. I had not considered that.
My concern with measuring the primary circuit is that it does not capture the actual heat going into the house which is likely to be less than the primary circuit due to mixing etc. Wonât this lead to an artificially high COP?
For COP/SCOP calculation, you want to monitor the total heat output of the heat pump, including losses in the buffer. Therefore, the COP will be lower than if you were to monitor the secondary side of the buffer.
The heat meter body will need to be on the primary flow before the diverter valve and the return temperature sensor will need to be after the last tee, see the section where the heat meter should be fitted in a system with a 4-port buffer highlighted on the diagram below:
As Glyn has explained, if anything itâs metering on the secondary side that would give an artificially high COP since that wouldnât account for the heat lost from the buffer.
Bear in mind the heat meter is only looking at the water flow-rate and the temperature difference between the Flow and Return pipes. Any mixing in the Buffer would increase the Return temperature back to the Heat Pump, so would get registered by the Meter on the primary side anyway.
You could add a second Heat Meter on the secondary side, but that would require a big investment. Maybe consider adding temperature sensors on the secondary pipework, to see how the primary and secondary flow and return temperatures compare with each other, from which it would be possible to infer details about the relative flow-rates.
Ideally youâd want a separate electricity meter just for the secondary pump (and any associated zone valve(s) and controls) - unless itâs straightforward to feed those via the Heat Pumpâs electricity supply.
Given I have 3 secondary pumps, each with their own zone valve, and those had been wired to a separate circuit breaker from the Heat Pump, I decided I wanted to check how much power they were consuming, so I added a separate electricity meter just for those. The results were disappointingly good: 59W with all 3 (Grundfos Alpha 2) pumps running and (Honeywell) zone valves open.
Thatâs a good idea. To minimise distortion losses across the buffer, you want the primary and secondary flow rates to match as close as possible. You wonât be able to measure the flow rate of the secondary (unless you fit a 2nd heat meter), but you can use the temperatures of the secondary flow and return to match to DT between the primary and secondary.
Itâs possible to add additional temperature sensors to the emonPi2 emonHP base station, when a DS18B20 temp sensor is plugged in it will appear in the Inputs in Emoncms:
Agree, a secondary pump(s) can have an effect on the COP. Even 59W running 24/7 is 1.4kWh/day which is equivalent to 5.6kWh of heat at COP or 4 which is about the amount of energy it takes to recharge a 200L DHW cylinder from cold.
Thanks Glyn - really appreciate your response - I am going to go with your suggestions, which make complete sense. At this stage I will go for the a single heat meter.
I hesitate to cloud the issue, but I think it may depend on what you seek from your monitoring.
If you are fixated on maximising your CoP (which Iâll define as Outdoor Unit heat output divided by Outdoor Unit power consumption), and can only afford a single heat meter (if your controller display doesnât already effectively do this at an acceptable accuracy), then the place to put it is on the primary circuit as @glyn.hudson advocates.
But if you want to understand where your heat losses are, and you want to balance your buffer tank properly, then you need a heat meter in the secondary circuit. Iâve put one in there and have discovered that 1) I get enormous heat loss in the transfer lines to/from the Outdoor Unit (up to 1kW which isnât actually getting to the house, so Iâll be having a word with my installer about the quality of his insulation), and 2) my secondary circuit flow was only half that of the primary, so I have been getting lots of short-circuiting in the buffer.
This latter means that I could maybe have dropped my LWT by a degree or two to get the same average emitter temperature - albeit at the cost of a little more secondary pump power - though I doubt that this energy saving will pay for the heat meter .
Personally, my goal is minimum electricity bills, not maximum CoP (but then Iâm just old-fashioned⌠).
Are you sure this is not caused by errors in the onboard monitoring if youâre comparing that to the secondary heat meter? Iâve found my onboard Samsung monitoring to have significant errors with the temperature sensing. 1kW is a huge amount to lose, unless your external insulation is very poor, and you have a very long run, I would be surprised if it was this high.
Adding a 2nd heat meter would be around ÂŁ200, while itâs a significant investment as a percentage of the installation cost and the potential running costs savings it maybe worth considering:
I read this as there already is a second bona fide heat meter present.
The heat loss on a lot of heat pump installations will be absolutely astronomical. All the spaghetti that the installers are fitting up the side of houses; through unheated attics and garages; and indeed even cylinders in unheated spacesâŚaussie style.
1 kW, especially in DHW mode, would not be surprising.
Even worse is the low quality (poorly insulated) underground pipework used on many installations. Once wet you effectively have underfloor heating outside. Even the good stuff (series 2 jacket size PUR/PIR which is a nightmare to bend) becomes rubbish once wet, and many installations do nothing to keep water out.
Thanks, @glyn.hudson, but it may be worth just reiterating that if you have glycol circulating fluid, you need a heat meter that can be calibrated accordingly (differing transport properties). The Axioma that you reference/sell appears to be water only (based on a quick read of the spec). If you have glycol, the Sontex series (e.g. 789) have good reviews, though they are more expensive (more like ÂŁ300 incl. VAT).
Ah yes, good point that is true. I assumed that since this was a new system it wouldnât be using glycol.
If possible glycol is best avoided for system efficiency and monitoring accuracy. Even if a heat meter is glycol calibrated thereâs a good chance the % mix wonât be totally accurate and will change overtime if the system is topped up with water.
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