Systemair VSR 500

[Stones]

I've been asked by another self builder to have a look into why their heating bills are significantly higher than they expected.  Part of the task will be checking the setting of their ASHP package (which is the same as mine).  They also have the following MVHR unit

 

https://www.systemair.com/xen/Villavent-UK/Products/residential-systems/rotary-units/side-connected/save/save-vsr-500-4f645bb8/

 

A quick look through the manual indicates it has an inbuilt electrical heater, which immediately raises the possibility of settings being in conflict with the main UFH heating from the ASHP, but also some strange defaults for an MVHR.  I'll know more when I've been and gone through the settings next week.

 

I've not come across a rotary heat exchange MVHR before.  Has anyone any experience of these / this unit and any particular advice / knowledge gleaned from experience?

[ragg987]

Can't help with this specific one, but our unit also has a heater built in and (if I have interpred the instructions correctly) it will come on only if the incoming air, post heat exchanger, would be below a set temperature. This is a user setting, I have set mine to 10C and it has not been used.

 

One thing I would look out for is occupant behaviour. For instance, when the other half is cleaning / vacuuming etc she likes to open the windows "to let fresh air in". Then a couple of hours later she says the house is too cold! Aaargh. It has taken a lot of reminding that even with all windows closed we are constantly getting warmed fresh air in the house, and that opening the windows on a cold day means the poor little 7kW ASHP cannot cope and dump sufficient heat like a 25kW gas boiler did in our old house.

 

Not sure if the message has fully got across yet...

[SteamyTea]

4 hours ago, ragg987 said:

Not sure if the message has fully got across yet...

Get them a very small engined car,  one that can do 70MPH, just.

Then load it up and send them on a trip.

The physics is almost the same.

Edited December 21, 2017 by SteamyTea

[MikeSharp01]

5 hours ago, Stones said:

significantly higher

How significantly?

[ragg987]

59 minutes ago, SteamyTea said:

Get them a very small engined car,  one that can do 70MPH, just.

Then load it up and send them on a trip.

The physics is almost the same.

Preaching to the converted here. She would be the first to admit that logic is not her strength.

 

BTW she has a 1.2l car that punches out 120bhp. Pretty impressive, I think back to a golf GTi I once owned that pushed out an impressive 118bhp. Them were the days...

[ProDave]

I will be interested to hear the answer to this.

 

Does the ASHP have any power monitoring i.e. to measure how many KWh it has used?  I don't think mine does so I plan to install a KWh meter for it so I have a measure of heating power independent of other electriciy usage.

 

My plumber friend initially complained of high heating bills. He got he heat pump installer back to check things over and they said it was "some wrong settings" on the mvhr. I don't know any more details.

[Jeremy Harris]

Rotary vane heat exchangers can give very high efficiency figures, they are the standard type of heat recovery system used on commercial buildings, the downside being that when scaled down there is another geared motor and slowly rotating moving part (the vane heat exchanger) that means that their efficiency doesn't scale well and smaller units are barely better than standard fixed heat exchangers, which is one reason that they aren't that common in domestic properties.

 

My guess is that the electric duct heater is coming on a lot, and that it may well be down to the way the unit is set up.  If there is a way to disable the duct heater, then that would probably be a good starting point.  In all probability the duct heater isn't needed in the climate up there, anyway.

[Stones]

30 + kWh per day more than anticipated, which immediately suggests they electric heater in the MVHR being the culprit, as it's rated at 1.6 kW.  That's been meantime disabled, but supply air is only being delivered at 14C, which again, looking at the manual, suggests the MVHR remains in its default settings.

 

I'll know more when I've actually had a proper look.

 

It does seem an odd design of MVHR for a domestic application, with another component that could fail. 

[ProDave]

That unit does look very much like the one my plumber friend had, particularly the control panel unit looks the same.  I wonder if the default settings make far too much use of the heater, hence your and my friend initially having high energy consumption.

 

Why do they refer to the heater as an electric heat battery? it is anything but a battery.

[dpmiller]

battery as in a series/ number of elements

[Stones]

34 minutes ago, ProDave said:

That unit does look very much like the one my plumber friend had, particularly the control panel unit looks the same.  I wonder if the default settings make far too much use of the heater, hence your and my friend initially having high energy consumption.

 

Why do they refer to the heater as an electric heat battery? it is anything but a battery.

 

That's certainly my suspicion. As I say, I'll have a better idea of what's going on next week.

[Jeremy Harris]

At a large scale, rotary vane heat exchangers are very good indeed, we had them fitted in the main air handling system of the large office/lab complex that was built as a part of the last programme I managed before retiring.  In that case the vane drum was around 2m in diameter and maybe a metre thick, with the vanes rotating slowly between the two sides, so they were warmed by the exhaust air then rotated so that the warm fins heated the incoming fresh air.  I can't remember the heat recovery efficiency, but it was up around 90% or so.

 

At the domestic scale I'm not convinced that having another rotating part makes sense, and I suspect the efficiency drops.  The other problem is that the vane rotational speed needs to be varied depending on the temperature differential and air mass flow rate on either side, so the control unit has to be able to measure the four temperatures, both the inlet and exhaust side flow rate and probably the humidity, and set the vane rotational rate to allow the most effective heat recovery.  If the vane drum rotates too slowly then efficiency is lost because the warm side vanes will reach max temperature long before they rotate to the fresh air side and if the vane drum rotates too quickly there won't be enough time for the warm side vanes to warm up to close to the extract air temperature before they rotate to the fresh air side.

 

Not an easy thing to set up, so I assume that the control unit has a fair degree of in-built intelligence to monitor all the sensors and set the drum to rotate at the optimum speed.  It goes without saying that these units are pretty fussy about being balanced correctly, too, and are upset by high winds.......................

Edited December 21, 2017 by JSHarris

[Stones]

A bit of an update on this, was out having a look at the installation this morning.  A couple of minor tweaks required in the ASHP setting, but in general that appeared to be working well / as one would expect.

 

The MVHR, is only delivering supply air at a temperature of around 9C, despite the target supply air temperature being set at 19C (electric heater disabled). The only setting I can see that may have an impact on this is the Temperature Control function (page 25 of the manual below) from which you can:

 

Set the proportional band (P-band) range for PI controller. Default value 5°C.

Set integral time (I-time) range for PI controller. Default value Off.

Shows output signal presented for the supply air temperature controller

 

http://catalogue2.systemair.com/FileHandler.axd?hash=i5xyl6WZaYShkC8GeJSvsg!!

 

The manual isn't very clear on how to set the P-band (i.e. what setting deliver maximum heat recovery) so I've left it with the owner to experiment on both the P-band and I-time settings and report back.

[IanR]

1 hour ago, Stones said:

The MVHR, is only delivering supply air at a temperature of around 9C, despite the target supply air temperature being set at 19C (electric heater disabled).

 

What are the extract air and outside air temperatures when it's achieving 9C?

 

Sounds poor unless very low outside temp and house not yet fully heated up... unless the MVHR is in Summer Bypass mode. Has it got the heating season correctly set.

[Jeremy Harris]

+1 to the above.  I've read that manual from cover to cover and being in summer bypass mode, for whatever reason, seems the most likely explanation for what's going on.  Second most likely explanation is that the sensors are not giving the true temperatures at the various locations, and that the displayed temperatures aren't the actual temperatures, although I think that's a bit of a long shot.

[Stones]

@IanR, @JSHarris   According to the controller, its not in summer bypass mode. 

 

Supply air temp was 9C, Extract temp was 11C, outdoor air temp was 4C, RH was 72%.  Weather wise, a clear, bright and still day.

 

I'm not sure where the extract sensor is located within the unit - measuring the temp of air extracted from the house or the temp of air being exhausted.

 

The house is of the same construction and insulation levels as mine. UFH throughout and whole house temp at 21C.

 

Reading the manual again, the only other thing I can think of are the frost protection settings, which are related to RH as well as outdoor temperature, although I do still wonder if the proportional temperature settings I referred to earlier, are part of the problem.

 

What I will say is that appears to be an overcomplicated system compared to the various counterflow MVHR units I've had over the years

 

 

 

 

 

 

[Jeremy Harris]

What's odd there is that the house is at 21 deg C, yet the extract temp is 11 deg C, which suggests that the extract temp sensor is downstream from the heat exchanger.   

 

The really odd temperature is that supply air temperature to the house, I would have expected it to be a lot warmer, unless the air flow rate is way too high.  Has the unit been set up and balanced properly?  Is it possible that there is far too much air coming in through the fresh air side and that it dropping the temperature?

 

 

 

 

[IanR]

I can't see that the Extract Air Temp is measuring what it should be.

 

As part of the commissioning was there a setting to identify which fan was which? It's possible this has been set the wrong way around and along with it the Sensors are incorrectly identified. It would make sense that 11C is the Exhaust temp rather than Supply Temp.

 

I know this one as I made this mistake myself!

[Stones]

25 minutes ago, JSHarris said:

What's odd there is that the house is at 21 deg C, yet the extract temp is 11 deg C, which suggests that the extract temp sensor is downstream from the heat exchanger.   

 

The really odd temperature is that supply air temperature to the house, I would have expected it to be a lot warmer, unless the air flow rate is way too high.  Has the unit been set up and balanced properly?  Is it possible that there is far too much air coming in through the fresh air side and that it dropping the temperature?

 

 

 

 

 

I would agree that temperature suggests the sensor is downstream of the heat exchanger, and looking at the internal component diagram, that does appear to be the case, which leads me to believe that the rotary heat exchanger is operating under some form of proportional control and hence not providing full heat recovery.  The odd thing is the position of the supply and outdoor sensors shown on the diagram...

 

Supply air flow is at its lowest setting, and balanced room to room according to the suppliers plan/figures.

 

 

20 minutes ago, IanR said:

I can't see that the Extract Air Temp is measuring what it should be.

 

As part of the commissioning was there a setting to identify which fan was which? It's possible this has been set the wrong way around and along with it the Sensors are incorrectly identified. It would make sense that 11C is the Exhaust temp rather than Supply Temp.

 

I know this one as I made this mistake myself!

 

I can't answer that one, but can probably find out. Do you have one of these units?

[IanR]

3 minutes ago, Stones said:

Do you have one of these units?

 

Nope, I have a small, commercial Airflow Unit. There was a setup step called "fan orientation" where you're asked to identify which is the Supply Fan. When I entered this wrong the controller swapped the Supply and Exhaust temps.