Posted by: @rhh2348

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Grundfos primary pump is still sending the water round at the same rate

Is the pump controlled to be variable speed? A second plug connected?

Not sure but believe the circulation pump speed is modulated to help manage dT. Sitting stationary may not do anything other than fixed speed.

 

Also see here

https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/ecodan-ashp-how-to-optimise-my-set-up/paged/7

Posted by: @rhh2348

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Looking for some guiding principles / a fuller-understanding here as not really sure what's right / going on!

Mitsubishi's default min/max settings for 'flow sensor' are 5 / 100.

Our Ecodan is reading from a Sika VVX20Mitsubishi flow sensor on the primary return before the filter.

The Mitsubishi manual states "*18 Do not change the [2 x flow] setting since it is set according to the specification of flow sensor attached to the hydrobox."

The Sika sensor states its range is "5..80 l/m".

Flow rate has been measured at various pump speeds using an 'analogue' flow meter.  With the FTC settings at 5 / 100, the Ecodan reports flow 2-3l/m lower than the analogue.

If the FTC settings are changed to 5 / 80 (to match the actual sensor, as Mitsubishi manual states!), the flow rate reported on the FTC goes down - anecdotally by up to 7-8 l/m.

The reported figures at 5 / 100 can be manipulated (up) to roughly match the analogue meter's flow rate if the FTC min flow setting is increased to 7.

 

Regardless of the min/max flow settings values and reported flow rate, the Grundfos primary pump is still sending the water round at the same rate (according to the analogue flow meter) - therefore does anyone have any thoughts on how the FTC should be configured and what effects (elsewhere) there might be if it were configured 'properly' (i.e. min/max flow at 5 + 80 per sensor) given the resulting lower reported flow rates?

Achieving an accurate flow measurement is probably the more difficult of the four main parameters.

As you state the Sika data shows the VVX20 standard model to have a specified flow range of 5 to 80 lpm, whereas the optional extra flow meter PAC-FS01-E detailed in the Ecodan manual would appear to have a specified flow range of 5 to 100 lpm. The output from both flow meters is stated to be 0.5 volts dc at 5 lpm and 3.5 volts dc at full range. By measuring the dc voltage output from the flow meter under steady flow conditions it should be possible to ascertain which of the ranges most accurately matches your analogue flow meter. Sika claim the accuracy to be +/- 0.75% at flow rates below 50% of full range.

What analogue flow meter are you using as a reference? What is its range and accuracy?

As I stated previously, the actual flow rate measurement is not that critical as long as it does not cause any alarms that stop the heat pump from functioning. I believe that the flow rate measurement may be used in estimating the thermal energy output of the heat pump, but this tends not to be too accurate on most heat pumps.

 

Posted by: @derek-m

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As you state the Sika data shows the VVX20 standard model to have a specified flow range of 5 to 80 lpm, whereas the optional extra flow meter PAC-FS01-E detailed in the Ecodan manual would appear to have a specified flow range of 5 to 100 lpm.

As mentioned above, the one I have 1) has the MITSUBISHI suffix after the VVX20, and 2) states 5..80 lpm on the front - I can't find much info or sufficiently-high res images of the part number you kindly advised, but would have expected the 'default' (or most-quoted) values to follow the standard part rather than the optional one. 

In any case, setting the FTC max flow rate to match the part's installed, as advised in the manual, reduces the value being read!?

 

The output from both flow meters is stated to be 0.5 volts dc at 5 lpm and 3.5 volts dc at full range. By measuring the dc voltage output from the flow meter under steady flow conditions it should be possible to ascertain which of the ranges most accurately matches your analogue flow meter. Sika claim the accuracy to be +/- 0.75% at flow rates below 50% of full range.

That's a good shout.

 

What analogue flow meter are you using as a reference? What is its range and accuracy?

It was a third party's; I don't have that information to hand now.

 

I believe that the flow rate measurement may be used in estimating the thermal energy output of the heat pump, but this tends not to be too accurate on most heat pumps.

Indeed - in limited testing it seems to have made a hugh difference to the delivered kWs being reported!  I guess, as long as the flow rate settings remain constant, the relative values are most important over the year.

 

@rhh2348

A vortex flowmeter is actually measuring the velocity of the liquid passing through it, which coupled with the actual area through which the liquid is passing allows the volume to be calculated.

There are recommendations as to how and where a flowmeter should be installed. Have these recommendations been followed?

Without knowing the details and specified accuracy of the analogue flowmeter, how do you know which flowmeter, if any, is providing an accurate reading. When testing any measuring device, the reference instrument should be at least 3 times more accurate than the device under test.

I would suggest that you make a note of the various controller settings before making any changes. You could then change the range from 0 to 100 lpm to 0 to 80 lpm and see how this affects the system operation.

@derek-m The man with a watch is confident he knows the time -the man with two watches … is never quite sure.😉

Posted by: @rhh2348

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The Mitsubishi manual states "*18 Do not change the [2 x flow] setting since it is set according to the specification of flow sensor attached to the hydrobox."

The Sika sensor states its range is "5..80 l/m".

The manual is quite explicit that it is set for the flow meter supplied ... and the Sika sensor says it only measures up to 80l/min - but if you look at the other side of the sensor you will see printed:

Pin2: U flow 0.5...3.5V
5...100l/min

So the maximum voltage would correspond to 100l/min, which is what you are telling the unit software it should work to. It won't ever get near that signal level as the pump supplied tops out at around 25l/min.

The unit will shut down if certain paramenters are exceeded, including being out of the acceptable flow rate range, so adjusting the values the software ascribes to the signal from the flow meter may have unintended consequences.

 

 

 

Posted by: @derek-m

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There are recommendations as to how and where a flowmeter should be installed. Have these recommendations been followed?

It's on the return before the mag filter so I assume so.

 

Without knowing the details and specified accuracy of the analogue flowmeter, how do you know which flowmeter, if any, is providing an accurate reading. When testing any measuring device, the reference instrument should be at least 3 times more accurate than the device under test.

Good points.

 

I would suggest that you make a note of the various controller settings before making any changes. You could then change the range from 0 to 100 lpm to 0 to 80 lpm and see how this affects the system operation.

Yep, already done/doing - though it feels like the effects on readings (e.g. lower delivered kWs, reduced HP power) are downw to FTC calculations rather than physical differences.  Will continue to vary + test and see what happens.

 

[Edit: removed Pin2 commentary as I've just seen @harriup's post!]

Posted by: @Anonymous

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Is the pump controlled to be variable speed? A second plug connected?

It can be controlled using PWM (profile A), yes, but we don't have a 2nd plug connected at present.

 

Not sure but believe the circulation pump speed is modulated to help manage dT. Sitting stationary may not do anything other than fixed speed.

I think this is the next area I'm headed to following testing, which I'm at the tail end of.  I've gone through all pump modes and (set) speeds to get closest to an optimal combination of: dT of 5, best CoP, power output, reheat speed, etc.  (More to follow).

I've seen on mine it modulates the compressor down a little, and infrequently, to seemingly-achieve this, but can anyone confirm they have experienced the FTC6 adjusting pump speed to optimise running operation (e.g. slow down flow C increases / increase dT)?

Furthermore, does anyone know how a Grundfos UPM3 would operate if under PWM control - does it map FTC speed 1 to lowest pump flow and speed 5 to highest and step up and down, or is it more-variable on the l/m??

 

Posted by: @rhh2348

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speeds to get closest to an optimal combination of: dT of 5, best CoP, power output, reheat speed,

My heat pump is a variable speed circulation pump, but it seems to do what you don't expect.

It doesn't seem to run a fixed dT. One of the issues is the heat pump tries it's hardest to stay running once it has started.

It initially runs full load to get the dT as close to target as it can. Then then back off, as return temps come back warmer it adds heat to try and get to target flow temp and keep dT stable. There will an overshoot hysterisis, it then starts working in that range. If it kept at dT that range gets consumed quite quickly (if running below min modulation). So it allows dT to reduce a little by increasing flow rate.

This is a run I noted when doing some commissioning 

14 degs OAT 

Target flow temp 27 overshoot hysterisis 0.4.t

50 sec into start 26.4 degs flow

90 sec 26.7 degs flow

At 2 mins down to 26.6 reduces load at 2.5 mins temp at 26.7

3.5 min at 27

4 mins 26.9 dT 4.9

5 mins 26.9

6 mins 27 dT 4.7 0.964 m³

7 min 27.1 dT 4.6 0.973m³

8 min 27.2 dT 4.6 1.021 m³

9 min 27.3 dT 4.4 1.02 m³

10 min 27.3 dt 4.3 1.03 m³

11 min 27.4 dT 4.4 1.036 m³

11.5 min trips

@johnmo

I think you will find that your results indicate the following.

All control systems have limits within which they can operate correctly, but once you go outside those limits then the control system can no longer perform correctly.

Within your controller it would appear that there are two individual control loops, one varies the compressor speed to produce the required LWT and also supply the thermal energy demand, while the other varies the water pump speed to produce the desired DT.

On start-up the controller senses that the LWT is below the desired value, so runs the compressor faster to produce more thermal energy. As the LWT starts to increase it creates a DT between LWT and RWT, but there will be a limit as to how high the LWT can increase until the RWT also starts to increase. As the LWT and RWT start to warm up, the controller starts to reduce the compressor speed and thermal energy output as it senses that the system is warming up. It would appear that the controller pulled back the compressor to its minimum operating speed.

Because the heat pump is still producing more thermal energy than that being emitted by the heat emitters, the net effect is that the RWT continues to increase, which in turn causes the DT to reduce and the LWT also to increase.

The LWT controller has now reached its minimum operating limit, so can no longer prevent the LWT from increasing. The DT controller has also reached its operating limit and can no longer maintain the DT at 5C, but now appears to be increasing the flow rate to try to prevent the LWT from continuing to increase. This it can do for a limited period of time, but because the heat pump is still producing more thermal energy than is required, the LWT continues to increase until it reaches the high limit and stops the heat pump.