The unit is quite different to the old Helios unit. A key difference is that is has a small (1kW) heater on the supply side so that once the heat exchanger has done it’s thing, the supply air is then heated slightly.
I currently have this set such that it heats the air to the same value as the extracted air - this is obviously an average of the house temp that ranges from 17 to 20.
The effect of this small amount of power (3-4kWh in 24 hrs - outside temp 1 - 10) is quite dramatic. Once the UFH went goes off in the morning, the main room would maintain the set temp for a while. What I am seeing is that it rises by a couple of 10ths. In the evenings, it looks like the room again maintains its temperature better. Both of these are presumably because the supply air temp is higher. The surprising thing to me, is the small amount of energy required to achieve this.
It is going to be extremely difficult to prove conclusively, but anecdotally, this is what I am observing.
According to the image, the heating energy is 3.28 kWh and the consumed energy is 4.85 kWh, so I suppose the energy used by the fans and any parasitic energy use due to ventilation is 1.57 kWh. Since that’s a daily total the average power is 65.4 W. The flow rate is only given as a percentage so I suppose it’s somewhere between 180 and 200 m³/hr. Even using the larger figure that makes the SPI 65.4/200 = 0.327 Wh/m³, somewhat larger than stated. I wonder what the cause of the discrepancy is?
4.2 kWh is the heating I’ve been putting into our house overnight during Jan and most of Feb. I’ve switched the heating off for now although I may put it on again a bit when the nights get cold in a few days. It is very interesting how the sunlight and external temperature interact and how much effect the internal temperature has on the exact heating required (or vice versa).
I think that figure might be a bit high. Fans are not usually linear I believe? I’d expect the SPI to be reasonably accurate. Ah and you also do not know how long that was (in the day) I posted it at 16:44 so not a full 24h period.
I have now had HomeAssistant adjusting the () supply ‘setpoint’ for a while to maximise efficiency  i.e. maximise the heat recovery without additional heating.
What I noticed, by monitoring the data with Emoncms was that using a fixed setpoint had some interesting consequences.
When  the supply air temperature from recovery alone was below the setpoint, the heater was in operation and when above it, colder outside air was mixed with the internal air to achieve the setpoint.
The automations I now have in place now do 2 things;
Check and see if the heater is on and if the setpoint is above my minimum, it will reduce the setpoint so the heater goes off.
Attempts to increase the setpoint if the heater is off so the maximum supply temperature can be achieved.
There is a tension between these two so there is a delay so that the changes only happen once every few minutes which also allows the change to have an effect.
As it stands, it has been fine until now in the heating season, but I need to modify these for the summer months. Firstly I need to add a max setpoint to the automation.
Secondly, I’ll need to add 2 modes (winter/summer) and add in automations for the summer so I can maximise the cooling.
The other thing, again by adding sensors and measuring, I could see the Fan was running way too high. Under normal circumstances, the fan is now running at 20% and it increases as the extract CO2 rises.
The value of measuring and recording data, and reviewing it cannot be overestimated!
That sounds a bit bizarre, or more exactly - naive. The idea that there is exactly one temperature that is comfortable and must be maintained is not terribly well-regarded I think. PH has the heating maintain a temperature of at least 20°C and overheating is defined to start at 25°C. Both are conservative IMHO.
Hmm, it sounds a very complicated way of accomplishing having a heater on when it’s cold and cooling when it’s hot (i.e. summer bypass open). But if it works…
My feeling is the implementation is a ‘thermostat’ setting i.e. this is the temperature I want - but I agree, not a good implementation.
Ah but that is exactly the opposite of what it does. The purpose is to maximise the heat recovery. If the setpoint is not raised, some of the heat that could be recovered isn’t.
The heater is simply the trigger I use as the system is switching the heater on when the supply setpoint is greater than the achievable temperature by recovery alone - it then decreases the setpoint until the heater is off. This is happening because I am raising the setpoint until it can’t be achieved by recovery alone (so drops back down again). Obviously, in the morning, the automations are increasing the setpoint and in the afternoon decreasing it (as it stands). In the summer, I will want a different sequence to keep the house cool.
As far as my knowledge about MVHR units go and according to the explanation of the designer of the heating/cooling system of my house, the MVHR is not inteded for heating/cooling.
The heating of the MVHR serves only the purpose of protecting the heat exchanger unit from frost, that means when the inlet air temperature (outdoor) is too low and the outlet of the heat exchanger (from indoor) would be too low and frost would build on the exchanger.
If you heat it too much, the recovery efficiency gets lower.
If you want to heat the house, a heating element after the MVHR is the solution (applied in some passive houses).
For cooling, the air transfer rate is very low (if you compare it with opening a bigger window) and the time window where it can be efficent is very limited (at least in Hungary, where I live).
There are units combined with a small ASHP for DHW. They can cool down the indoor air/outdoor inlet, but those are another case.
My system has a small “radiator/calorifer” built in the outdoor air inlet side, with water.
It can heat the inlet air (to prevent frost) or cool the air in the summer. Cooling is passive cooling (using the same fluid/source as my ground source heat pump).
My MVHR is a very simple/dumb one (Atrea Dupley Easy 300). I cannot set the temperature for summer bypass (is probably set for 20°C) and can only set the fan %. But with having a CT on the circuit for the unit, the power consumption is aroung 15W for 20%, and 30W for 50%. That makes less than 1kWh for a day for the around 90% recovery efficiency.
The heating system also has a summer/winter mode changer. It is a simple thermostat on the outdoor temperature. In my case, above 25°C is “summer” (cooling), below is “winter” (heating). Make sure to use some hysteresis. Mine has hysteresis set for -5°C and 15 minutes.
You’re quite right that the main purpose of an MVHR unit is reducing pollutants to increase air quality, and heating or cooling is not the main purpose. My system has a pre-heater for frost protection and I’ve added a post-heater to heat the house as you suggest. Brian’s system is a little unusual since it has a different arrangement.
His system has a built-in post-heater that by default tries to maintain the temperature of the supply air at a setpoint. Our discussion is about the complications of using an external computer control system to maximise the efficiency of the device.
From reading the manuals, I think it may be possible to disable the post-heater by setting ‘eco’ mode. That might be a simple way to reduce its operation, Brian?
Here in the UK, I’ve found there are significant periods in the spring and autumn (like for the past month) when the summer bypass opening and closing automatically and mainitaining our house at a comfortable temperature. (It’s a PH.) Once summer comes we’ll open some windows and in the winter I’ll use some heating. I have my bypass set to open at 24°C and I’ve set a 1.5°C hysteresis so it closes at 22.5°C. That seems to work fairly well for us. One of the complications with Brian’s system is that it doesn’t seem to allow any hysteresis by default. Instead it tries to maintain an exact setpoint either by heating the supply air or by blending in some outdoor air. Both actions reduce the efficiency so Brian is trying to control the device better.
Yes true, but the other point is to recover as much internal heat as possible (i.e. return the heat to the house) during the heating season. I discovered that, as designed, this control system did not do that.
Yes and there is a small 1 kWh element on the supply side - it is this I am using as the trigger for the automation. In winter, once I reach my minimum setpoint, it will kick in more (only installed since end of Feb).
Again true, but there is little point expelling cool air to bring warmer air in.
I am hoping that I can prevent that - time will tell - but my current ‘winter’ system will not
I am not trying to totally preclude its use (and yes I was aware of the Eco mode), I am using it as a trigger. When the internal controller decides it cannot maintain the supply setpoint just by recovered heat, it switches the heater on (as expected). My automation says “Oh, you switched the heater on. Ah, but we are above the minimum setpoint so if I reduce the setpoint you will switch the heater off”.
Ideally the controller would have a max/min setpoint so it did this itself. It does have other modes, but none that maximise the recovered heat.
If it is true hysteresis, if closed it will open at 1.5° above the set point and close 1.5° below. Hysteresis should not be confused with max/min.
If it is going to be warm, I don’t actually want it to get that high so I will try and maintain the coolness from early morning. If the outside air temperature is warmer that inside air, opening windows just lets in hot air.
Yes and no. What it needs is a max/min (with hysteresis around each point to prevent cycling)