Observations Commissioning ASHP

[JohnMo]

Long while no update.

 

Messed about with hybrid (gas and ASHP) last winter and after doing the total running costs, decided I was approx £100 plus to have a hybrid system, mostly due to additional standing charges - so gas has to go. Meter being disconnected tomorrow, by Octopus at zero cost to me.

 

Ignoring the hybrid settings, current settings are 

No thermostat, WC on heating and WC on cooling (very small amount of 0.5 Deg flow temp change). Change over (between heat and cool) by a single repurposed light switch.  In addition to that I have a second set point which adds 3 degs to heating curve and 1 Deg is removed from cooling curve, this activated by a Shelly relay if I have excess solar PV.

 

CoP when running has been great, high 4s to high 5s. When coupled with standby time it hasn't been the best (measuring all electrical input in the ASHP system and heat meter). So heating CoP overall was mid 3s. Cooling high 3s.  However between heat pump cycles the circulation pump was kept on, with pump, valve, performance monitoring and other stuff drawing 117W during standby. Switching the pump off with everything else on, brings the standby down to 31W. 

 

So to fix the issue I have implemented the circulation pump to run in sniffer mode, so circulation pump runs for 4 mins after heat pump compressor has stopped and then stays off for 40 minutes, before starting again.  If heat pump senses the return temp isn't within limits the heat starts again.

 

Current running cooling and in the last 24 hrs including one DHW heat cycle at night (15 degs) the daily CoP has increased to 4.91.

 

A similar average temp day a week ago the CoP was 3.88, with one DHW cycle in the day at 20 degs. So CoP has increased a full point. Rough calculation is a saving of about £50 per year.

[-rick-]

Good result.

 

I assume you are just running the pump in an on/off form. Any thoughts about speed control? Reason for mentioning is when I've thought about what I might want to do, if it ever happens, is that the pump might serve as a useful way to distribute heat/cold between rooms to try and keep things equalised despite some rooms having higher heatloss/gain than others.

 

Edit: Clarification, idea being that to do that equalisation you'd likely want to run the pump more than for a short period every 40 mins. Running slow for longer might be better than more frequent full on pulses. I've done no maths on this as don't want to start detailled work until I actually have a project.

Edited July 9 by -rick-

[JohnMo]

5 minutes ago, -rick- said:

Good result.

 

I assume you are just running the pump in an on/off form. Any thoughts about speed control? Reason for mentioning is when I've thought about what I might want to do, if it ever happens, is that the pump might serve as a useful way to distribute heat/cold between rooms to try and keep things equalised despite some rooms having higher heatloss/gain than others.

The controller does all the on off stuff, the pump also run variable speed, more so in heating than cooling. It has various control strategies for the circulation pump. So it's currently on periodic running and proportional regulation.

 

 

An hour or so of the data from the heat pump monitor 

The flow rate is the light blue line. Speed control works trying to control dT. 

 

My main reason for running 24/7 was to distribute heat evenly, but the intermittent nature doesn't seem to affect the way the house feels. So at the moment I see no reason to pay for it to run it.

 

 

[ReedRichards]

Are you sure your cooling actually has an effect?  On another thread, you suggested that because it was 30 C outside and 22 C (or so) inside that it did, but I achieve exactly the same with no cooling whatsoever.  I presume this is because the thermal mass of my house keeps the inside temperature nearer the average outside temperature rather than following all the outside peaks and troughs.  We also use window blinds to limit solar gain.  

[JohnMo]

2 minutes ago, ReedRichards said:

Are you sure your cooling actually has an effect?  On another thread, you suggested that because it was 30 C outside and 22 C (or so) inside that it did, but I achieve exactly the same with no cooling whatsoever.  I presume this is because the thermal mass of my house keeps the inside temperature nearer the average outside temperature rather than following all the outside peaks and troughs.  We also use window blinds to limit solar gain.  

Yes definitely has an effect. The floor surface temperature is maintained at around 18 degs through out the building. We have massive windows 30m²+ in the lounge. Compared to pre heat pump cooling, when we struggled to keep room temperature in check, would get to 27 most sunny days and that was with the blinds closed. Now even when it is hot air temperature wise you feel it's cooler. Room temperature doesn't get as hot and it recovers relatively quickly. It's not Aircon, but you also don't have a continuous draft either. Makes the house a comfortable environment to be in. Without the need for external blinds etc.

[marshian]

On 17/07/2024 at 15:48, JohnMo said:

Forgot to include the weather compensation curve.

 

It starts at 10 degs OAT at a target flow temperature of 26 degs and goes down to -5, where flow is 31 degs. So flow temperature increases 0.33 degs with every degree drop in OAT. 

 

Really interesting @JohnMo  and prompted me to work mine out - good way of looking it it

[JohnMo]

So over the last 5 days, things have remained stable with daily CoP. Generally sitting at around 4.8 to 4.9. the dots on the graph are the daily average CoP. The purple line average daily temperature.  The chart below is for all running and standby etc for cooling and DHW, including powering a WiFi extender, all monitoring stuff.

This what the chart looks like if I only include the CoP for cooling while running and no standby.

So even though the CoP while cooling is lower than before, it's been the hottest day time temps so far this year at around 30 Deg.

[JohnMo]

After the minor change to circulation pump settings and leaving a week to settle in, thought I would check the heat pump monitor SCoP leader board to see how my system looked compared to others. So currently sitting 9th overall based on 7 days of figures

 

 

Mine is Maxa i32V5.

[JoeBano]

I wonder how many on the list are actually doing cooling aswell? Done well tweaking your settings. 

[JohnMo]

56 minutes ago, JoeBano said:

I wonder how many on the list are actually doing cooling aswell? Done well tweaking your settings. 

Quite a few are, some of the ones above me in the chart are still doing heating - in England, many aren't doing DHW lol.

[JohnMo]

Looking to do some automation to switch between heat and cool.

 

Currently just a simple on-off switch, works but... So been playing with ChatGTP and bouncing ideas about different things. I have a Polypipe UFHMCPS controller, which is only used for monitoring and recording room temperatures and as a DHW timer.  Also have a few unused shelly relays.

 

ASHP uses a zero volt switch, closed is heat open is cool.

 

Some good features of the polypipe controller are weather dependent heating control, fully adjustable hysterisis of room sensors.

 

Weather dependent control allows a set outside temperature, to make heating possible and you can adjust average time the outside measured over, from 1 hour to 24 hrs.

 

Room sensors can be made to switch heat on with an adjustable hysterisis from 0.1 to 5.0 degs.

 

So the scheme I worked through with ChatGTP is as follows 

 

Switching between heat and cool

An average 10 degs outside temperature to allow heating permissive. Coupled with house temperature of 23 (-) 3.5 degs hysterisis.

 

Heating system run pure weather compensation, so is never off just in heat or cooling mode, nothing in-between.

 

So this allows heating to switched on, only if below an average of 10 degs outside AND house temperature drops below 19.5 degs. Heating (cooling on) will only switch off if house temperature goes over 23 or the average outside temp goes over 10 degs.

 

Conversely cooling comes on when average temperature outside drops below 10 and/or if house goes above 23.

 

To enable switching, I need to do a wireless switch, so a shelly plus1 at UFH controller with the SW contact is connected to the live pump terminal. The pump L terminal being live when heating is asked for and off when it's not (so cooling is). A second shelly in disconnected switch mode, that open or closes the relay output, which is connected to the heat pump.

 

Nothing done yet just a thought process.

 

Have I missed anything obvious?

[JoeBano]

Sounds complicated? I know you probably want to use what you’ve got but heatmiser fan coil stats are good 

https://heatmisershop.co.uk/app-control-fan-coil-thermostat/

It has 1 call for heat and 1 call for cool, used a relay to switch a volt free connection on my heat pump. Has a 2c deadband, my set up is heat to 20c and cool from 22c, flick automatically from each with both having weather compensation. If you get the neohub you can automate IFTTT app with octopus energy rates and local weather forecast, this service is all free.  

[JohnMo]

2 hours ago, JoeBano said:

Sounds complicated? I

Think it reads more complicated than it is. UFH controller has weather monitoring built in with an already installed outside sensor it senses room temperature, so using it to switch between heat and cool.

 

2 hours ago, JoeBano said:

2c deadband

Do you get any undesirable switching between heating or cooling or is quite stable once switched over?

[JoeBano]

Not been a problem yet, have both heating and cooling on weather compensation so they shouldn’t hit the desired room temperatures on the stats. I suspect hot days and cold nights in autumn maybe a different story but I’ll see how it goes. I can change the deadband higher if needs be. 

[JoeBano]

How’s does your Ufh weather compensation affect your heat pump one? 

[JohnMo]

2 hours ago, JoeBano said:

How’s does your Ufh weather compensation affect your heat pump one? 

It doesn't. The UFH controller isn't connected to the UFH or heat pump. It has an external sensor. It allows the heating to be switched on only when average temperature is below an average temperature threshold and switches off the heating when above that. In my case I will use 10 degs average temperature over 24 hrs. Using a room sensor set to 23 (hysterisis set to 3) will complete the logic and will energise the UFH pump to start, (if I had one). I am just tapping the pump live signal to energise a relay.

 

So logic becomes, below 10 degs outside and below 20 degs inside heating comes on, stay on unless house temp exceeds 23 degs or it is warmer than 10 degs outside. All other times cooling is on.

 

All the heat pump will see is the opening and closing of the volt free contacts to select heat or cool.

 

 

 

[JohnMo]

Been asking ChapGPT loads of ASHP related questions. One was related to the use of ball valve strainers (which I use) and proper inline filters (I had a Spirovent Dirt on the boiler, now sitting idle). The main comment was on pressure drop differences. Spirovent being almost zero even sized at 22mm compared to quite high on the ball valve strainer.

 

The other question was heat pump run time, exploring UFH affects and water volumes. Short answer, as expected more water volume is better.  System volume is circa 70 to 80L without volumiser. In cooling mode first run of the day was typically 12 to 14 mins, no longer.

 

Have now installed an additional 50L water volume (around 130L total), used a cylinder that was used on the combi boiler as solar preheat for DHW. Not ideal in theory as it only has 22mm ports. The only place I could install due to layout issues was close the the ASHP. It is connected within the return piping as a volumiser. This means without mitigation the volumiser would get filled with DHW heating water - not ideal. So used a previously used ESBE Mixing valve as a diverter driven by the relay, I use on DHW signal filtering. Added the Spirovent filter while I was there.

 

First run I left the strainer in place as well as the Spirovent, flow reduced from the 19.5L/min to 16L/min, which was worrying. However removing just the strainer from the ball valve flow jumped up to 22.5L/min. Ball valve strainers seem to be pretty rubbish and many get installed. So gained an extra 3L min flow while installing a 22mm volumiser and associated piping plus a 22mm 3 port valve.

 

Run time after volumiser install is been dramatic. Normal first run of the day is 10 to 15 mins, today 42 mins. CoP has increased (like for like outside temp) a small amount 0.04, not big put running CoP was already high, so now achieving 6.53 this morning while running. dT has dropped from 4.4 to 3.8, so this allows me to reduce flow target temp a little and get the same heat transfer, which will reduce run time a little but gain CoP.

 

Still need to complete the insulation, need some additional materials.