Thanks for the data, very interesting.

What do you mean by 'a way of decreasing the sensitivity'?

One of the weaknesses with weather only compensation, is that it makes no allowance for other factors, and in particular does not respond to changes in indoor temperature. I feel that weather compensation with auto adaptation would provide a much more constant indoor temperature, and may slightly reduce energy consumption. It should also allow you to easily change the indoor temperature up or down, should you find that necessary.

@derek-m,

(moved this reply to the right place)

I just meant a bit of a buffer on the target flow temp to stop the ASHP cycling so much.

I agree about the auto adaptation; I'll have think about it.

Kev

@kev-m 

Hi Kev,

If you look under '7. Main remote controller operation'. Page 38.

Then '<[Operation settings]> - Heating operation', you will find a table.

The bottom section are the settings for 'Heat pump thermo diff. adjust'.

If my understanding is correct the settings allow for the variation away from the calculated water flow temperature at which the heat pump starts and stops. So, if the calculated water flow temperature is 36C, and the Lower Limit is set to -5C, then the heat pump will start when the water flow temperature falls to 31C, and if the Upper Limit is set to +5C, then the heat pump will stop when the water flow temperature reaches 41C. The larger the difference between the Lower and Upper limits, the longer the time between the heat pump stopping and restarting. Having a wide setting may cause the indoor temperature to 'sawtooth' slightly, and I'm not certain what effect it would have on system efficiency.

@derek-m ,

Derek,

thanks, I'll have look at that.

Kev

Posted by: @derek-m

@kev-m 

Hi Kev,

Whilst going through the manufacturers data I noticed various aspects, which you, and other 14kW Ecodan owners may find of interest.

The first thing that struck me was that the unit could produce its full rated 14kW output, over the full range up to a water flow temperature of 55C at ambient air temperatures down to -10C. So a correctly sized unit, should be able to satisfy the heat demand over the vast majority of weather conditions that may be experienced in the UK.

It would appear that the unit has also been optimised for maximum efficiency in the Mid (11.2kW) to Nominal (14kW) operating range, which of course is more desirable when the unit is working harder during colder weather.

The modelling tool shows that a unit (based on your operating parameters) would go from cycling to continuous operation at an ambient air temperature range of 7C to 8C, which is what you found in practice. It would therefore be useful to see how closely the other parameters compare with the modelling tool.

The modelling tool should also help define the parameters for setting the weather compensation curve. In your case it is suggesting a water flow temperature of 43.7C at an ambient air temperature of -7C, and a water flow temperature of 22.8C at all ambient air temperature of 20C, which should produce an indoor air temperature of 21C.

If you should require a different indoor air temperature then get the settings from the relevant table in the Detailed Data sheet.

 

 

I noticed that too; in fact it can produce more than 14kW under some conditions.  Having said that, 14kW at a COP of 1.75 is 8kW - I wouldn't want to be paying the bills for that.  

I agree about the best efficiency; I think for me the ASHP will be running at the lower end a lot of the time.  It does make me think whether I could have got away with a smaller ASHP.

I'll have another look at the curve settings.  At the moment flow temp it looks a little cool at the higher ambients.

Kev 

@derek-m,

Derek,

I've had another fiddle round with the MMSP sensor; I've found a suitable copper pipe to attach it to.  It seems to be recording a realistic return temp so we'll see how it goes.

However...  I think the ASHP sensors - the ones that record flow and return for the ASHP rather than the ones for the MMSP heat meter - are under-reading. The MMSP heat meter currently says 36C flow and it's 4-5C outside now.  My Melcloud readings - which are from the ASHP - were never more than 32C flow overnight, when it was 1-2C.  Also, when my DHW kicks in, the max flow temp in Melcloud is 42C, even though my tank is set to heat to 50C. Finally, I bought some cheap aquarium thermomers (which seem surprisingly accurate) and taped one to one of the radiator inlets and it's also more than the Melcloud readings.  

If this is right, when the weather compensation is asking for a flow temp of say 30C, my ASHP will be producing maybe 36C.  

I think this may be because these temperature sensors are zip-tied to plastic pipes.  Plastic is a good insulator so the outside of the pipes won't get as hot as quickly, will they? 

@kev-m 

Hi Kev,

It looks like we are transforming you into an Engineer, you are beginning to think about what the sensors are telling you and what is actually happening within the system. You may soon be able to buy a mug that states 'I'm an Engineer, what's your Superpower?'. 😎  

I have been dealing with sensors and Instrumentation for over 50 years, and one thing that it is always important to remember is that equipment does not always tell the truth. Even when sensors are installed in thermowells (pockets), unless they are making good thermal contact there could be inaccuracy in the measurement.

Thinking of your concern about cycling, I was going to suggest that you check the location of the sensors connected to the FTC controller. If they are measuring the temperature in pipework that cools down fairly quickly, then this could lead to your ASHP starting and stopping more frequently than is necessary. I would suggest that you see if there are any recommendations in the manual as to where the sensors should be located. You could also use your newly purchased test equipment to investigate more appropriate locations for the sensors.

On my home heating system, when the boiler and water pump first start to operate, the sensor I have connected to one of the radiators initial shows a fall in temperature. This is because the water in the pipework under the floor has cooled faster than the water in the radiator, so initially a slug of colder water goes through the radiator before the warmer water arrives from the boiler. If your FTC controller periodically runs the water pump to check the water flow temperature, then it may be that your sensor is also seeing a slug of cooler water. You may be able to check this by monitoring the temperature indications when the pump starts.

Is your MMSP now functioning correctly?

No, still not working. ☹

The energy meter manual is very specific about these sensors and how they are positioned.

The FTC6 manual says where to install the sensors but not how. 

I think I need another chat with the installers.

Well the COP is now showing about 6.5, which I still don't believe.

Posted by: @kev-m

Well the COP is now showing about 6.5, which I still don't believe.

 

Hi Kev,

You should never get the Cops involved if you can help it. 😊 You had a COP of 20 the other week, so you are making things worse. 😯 

Is this the COP shown on the FTC controller?

It would be useful if you could go through the menu for the MMSP system, and record all the displayed parameter readings, so that it may be possible to identify what is working and what is not.

I have been thinking whether a Skype call would be more beneficial than repeated messages. Let me know what you think.

I have been reading through the two documents that you posted, and one of the things that is obvious, is that installers of ASHP's and MMSP systems have no idea about the correct use, installation and location of sensors. You can have the most expensive equipment in the world, but put the sensors in the wrong location and the measurements are all worthless.

I suggest that you try to draw a schematic of your system, showing the location of the equipment and all the sensors. With a few simple tests, it may then be possible to decide where the sensors should be located for correct measurement and operation of your system.

Derek,

the Ecodan controller increments once every 24 hrs and stores month and year to date, so you can't see it working in real time. 

Melcloud is showing flow at 31C.  My new precision HVAC instrumentation set (cheap Amazon aquarium thermometers sellotaped to the inlet pipe on the kitchen radiator) says 36C. 

It's all falling into place now. The last two weather compensation curves I've tried seemed like sensible numbers but made the house far too hot until I shifted them down on the controller.  That's consistent with the sensors under-reading.

I'll have a look at modiying the diagram I did before. 

Skype might be a good idea at some stage.  

Kev   

@kev-m 

Hi Kev,

I think that you said before that you don't have a buffer tank, but do you have a low loss header?

Do you have any pumps in addition to the one inside the ASHP?

For the sensors that are zip-tied to the pipework, once we find out what type they are it may be possible to either ask for them to be replaced by your installer with pipe clamp type or the installation of thermowells. First it is necessary to find the best location, so that they are providing both accurate and consistent measurements. See if there is any writing or labels on the sensors connected to the FTC controller to identify them. They could be a PT100 or PT500, which can easily be sourced at quite reasonable cost.

@kev-m 

Sorry Kev, I did not make myself clear in the earlier message. If you look through pages 6 through to 9 for the MMSP flowmeter, it shows how to obtain readings of numerous parameters, including temperature and flow values. From these it should be possible to see if everything appears to be working correctly, and possibly calculate the heat energy output. There is also a simulation mode, which should allow the setting a specified heat energy output, so that it may be possible to check if the FTC controller is receiving the data and doing the correct thing with the data once it has been received. You obviously need to record the MMSP flowmeter parameters when the ASHP is running.

On the FTC controller it should be possible to read the instantaneous flow and return temperatures, though I can't remember which screen it is on.