Panasonic Air Rads - be warned

[NSS]

We have a Panasonic Air Rad for spot heating/cooling in the one bedroom upstairs. Since commissioning the UFH and moving in it has stubbornly refused to work and, after consulting Panasonic, it transpires that the unit has a water temperature probe that will not activate the fan until it detects water arriving at the unit at 35C or above. As we only put water into the heating circuit at circa 31C max, we are simply not reaching that threshold. To my amazement, there is no provision on the unit to vary that 35C trigger.

 

Panasonic's initial suggestion was to raise the input temp to 40C. This is not only undesirable due to the fact that the ASHP would be working less efficiently at that temp, but the UFH circuits downstairs would quickly raise the floor temp above the limit of 27C (ish) dictated by the Karndean flooring. 

 

After numerous conversations with Panasonic over the last month, we were no further forward. I then spotted a paragraph in the manual that suggested it may be possible to operate the fan with the temperature probe disconnected. Panasonic were sceptical but today I gave it a try and, hey presto, it works.

 

Anyway, main reason for posting this in case anyone is thinking of using Panasonic air rads and is made aware of / put off by the 35C threshold (we weren't told before ordering it), it is in fact possible to overcome this.

[Guest Alphonsox]

We installed a Dimplex SmartRad in one of the rooms - very similar to the Panasonic Air Rads .This has the same fixed low temperature fan cut off arrangement but operating at 14C. A 35C threshold seems extremely high.

[NSS]

7 minutes ago, Alphonsox said:

We installed a Dimplex SmartRad in one of the rooms - very similar to the Panasonic Air Rads .This has the same fixed low temperature fan cut off arrangement but operating at 14C. A 35C threshold seems extremely high.

Yep, that's what we thought. The Panasonic can also do cooling though and is preset to only run in cooling mode if the water temperature is below 20C but it still seems a big differential between the upper and lower thresholds. 

[dpmiller]

depending on the sensor, a series or parallel resistor might be useful here.

[Jeremy Harris]

I'm a bit puzzled.  We run our UFH with a flow temp of around 25 to 26 deg C, but run the ASHP flow at a fixed 40 deg C, as that seems to give the best COP in practice. 

 

So, why couldn't the Panasonic Air Rad have been plumbed directly across the ASHP flow and return?

Edited December 6, 2017 by JSHarris

[NSS]

Just now, dpmiller said:

depending on the sensor, a series or parallel resistor might be useful here.

Panasonic had suggested this was a possible fix, but could not officially sanction it and intimated that doing so would void the warranty (whereas their manual states that it's possible to run it with the probe disconnected so no impact on warranty). 

[NSS]

2 minutes ago, JSHarris said:

So, why couldn't the Panasonic Air Rad have been plumbed directly across the ASHP flow and return?

It is.

[ProDave]

6 minutes ago, JSHarris said:

I'm a bit puzzled.  We run our UFH with a flow temp of around 25 to 26 deg C, but run the ASHP flow at a fixed 40 deg C, as that seems to give the best COP in practice. 

 

So, why couldn't the Panasonic Air Rad have been plumbed directly across the ASHP flow and return?

And why would increasing the ASHP flow temperature overheat the UFH? does that not have it's own blending valve?

[Jeremy Harris]

Just now, NSS said:

It is.

 

 

So why not just wind down the mixer on the UFH and wind up the setting on the ASHP to a tad over 35 deg C?

 

Running the ASHP under 35 deg C isn't going to make it run more efficiently, if lightly loaded and set at such a lower flow temperature it will probably be running less efficiently, as the differential temperature between flow and return is likely to be pretty low.

[NSS]

3 minutes ago, ProDave said:

And why would increasing the ASHP flow temperature overheat the UFH? does that not have it's own blending valve?

Pass ??? 

[NSS]

Okay, thanks guys. Seems I need to have a chat with the UFH installer.

[Jeremy Harris]

It's something you can probably do yourself.  On the UFH manifold there will be a thermostatic mixer valve, either a two or three port one, that sets the UFH flow temperature.  We have a simple two port one, you can see it here, the white control at the left of the lower manifold, in the centre of this photo, where the flow comes in from the ASHP:

 

 

Then, when this is set to give the desired UFH temperature, the ASHP flow temperature can be adjusted upwards. I'd suggest setting it to around 40 deg C, as I found that seem to work very well for ours.

[NSS]

Nope, we have nothing like that on the manifold.

[Jeremy Harris]

They do come in different shapes and sizes, but all do the same thing, they ensure that the UFH runs at the set temperature, irrespective of the heat source temperature.  Yours may be a smaller three port blender valve, with a smaller control.

 

I've not seen a UFH manifold without a form of temperature control valve, either a two port one like ours, or a three port one.  The three port ones look very much like the ones used on thermal stores or other hot water storage systems to control the DHW temperature.

 

The UFH flow temperature needs to be adjusted to give just enough heat to the floor to warm the house quickly enough, without too much overshoot, just for comfort.  Having a high UFH flow temperature tends to result in greater swings between the maximum and minimum room temperature, as it takes time for the heat to get from the UFH pipes to the floor surface, so if the UFH pipes are running too hot, the heat will continue to soak out to the floor for a long time after the thermostat has turned the heating off, resulting in the rooms continuing to warm up for some time.  We suffer from this if the flow temperature exceeds about 26 deg C; as long as I keep the thermostatic valve set down below that level things are fine.

 

The ASHP flow temperature, just like any other heat source, needs to be set to give best performance at the load it is operating at.  Running an ASHP at too cool a flow temp will tend to cause the unit to modulate down to a low level, all the time,  and never operate at it's most efficient temperature.  One key point is to get the difference between the flow and return temperature of the ASHP up to a reasonable level, as this sets the modulation level and also has a significant impact on the anti-short cycle timing.  If the ASHP is running with the anti-short cycle system kicking in a lot, then it's efficiency will drop because of all the additional starts and stops, especially in milder weather, when the heating isn't being required to deliver much heat.

Edited December 6, 2017 by JSHarris

[NSS]

The only thing that sits across the flow and return sides to/from the manifold is this thing.

 

[Jeremy Harris]

It's not that, the thermostatic mixer valve is almost always directly mounted on the manifold and UFH pump itself, or very close to it, either as shown in my photo or as in these photos of other UFH mixing valves, taken at random from the web:

 

 

 

 

 

 

The mixing valves are all at the bottom or lower left of each photo, with a temperature control knob.  There is almost always a thermometer in both the flow and return manifolds to, to allow the UFH to be set up properly to give the desired differential temperature between the UFH flow and UFH return (not the same as the ASHP floa and return, they are separate; not all the flow from the ASHP goes through the UFH all the time, when the thermostatic valve senses that the UFH flow is at the set temperature it throttles back the flow and so some of the ASHP flow goes through the bypass, buffer tank, other heating appliances in the circuit etc, at the ASP set flow temperature.

Edited December 6, 2017 by JSHarris

[PeterW]

52 minutes ago, NSS said:

The only thing that sits across the flow and return sides to/from the manifold is this thing.

 

 

Thats a low loss header ....

 

Got a photo of the manifold itself and the pump that drives the flow around the circuits ..??

[NSS]

This is ours manifold

 

 

[PeterW]

So basically all your floor loops are directly linked to the ASHP and the pumps only run when the ASHP is on. 

 

Hence why you can’t change the flow as it’s the ASHP that is dictating the flow temperatures. 

[Jeremy Harris]

@Nickfromwales may add to this, but I've never, ever, seen a UFH manifold configured like that.  I did loads of research before installing ours, and every single manifold system I looked at had the pump and mixer valve across the manifold.  None had another pump is series with the ASHP pump (assuming your ASHP has an integral pump; most seem to).

[Nickfromwales]

32 minutes ago, PeterW said:

So basically all your floor loops are directly linked to the ASHP and the pumps only run when the ASHP is on. 

Not quite. 

The UFH can circulate from the low loss header ( spot on with that btw ) as it hydraulically separates the UFH from the ASHP. That allows each circuit to remain at 0 poreabtail and each can pass through the LLH without either pulling or pushing in any direction. Both 'can' therefore circulate independently, but there should REALLY be a 2-port zone valve in that arrangement which opens when the ASHP is called on for heat. That imo would offer a better heating characteristic / hysteresis as it would circulate the heated water rather than heat linear to the ASHP set temp ( and its hysteresis). 

I agree that the likelihood is that it's all running in unison, and it's very strange to see it configured this way, as @JSHarris has highlighted. 

@NSS, does the ASHP also provide DHW ?

[ProDave]

I briefly questioned whether to run the UFH without a blending valve and simply set the UFH temperature by setting the buffer tank temperature, but the consensus was that was a bad idea.

[Jeremy Harris]

TBH, I doubt that the low loss header is doing much, if anything.  They all have a lowest operating  power rating,  which is set at boiler type temperatures (it's why they were designed - to deal with the minimum flow requirements of boilers).  When run below about 40 deg C I doubt that the minimum power rating for that low loss header would be achieved (it looks as if it is a 30 to 40 kW minimum power rating one to me, probably rated at about 60 to 65 deg C).

 

I reckon this system was installed by someone who usually installs radiator systems, where the flow temperature is controlled by the boiler heating thermostat, as that's exactly how it seems to have been set up. 

 

The good news is that reconfiguring it to with the pump circulating around the UFH, with a valve (as @Nickfromwales suggests to be able to turn off the return from the UFH) and a mixer valve added to set the UFH flow temperature  looks to be reasonably straightforward.  The pump can probably be re-used, a mixing valve would need to be added, plus ideally thermometers on both manifolds, and some reconfiguration of the pipes and wiring would be needed, but you would then get a system that would undoubtedly be more flexible, more efficient and allow the air rads to work normally, with a higher output if that is needed.

Edited December 6, 2017 by JSHarris

[SteamyTea]

Just so that I understand what is going one.

 

These mixer valves allow the fluid to be circulated around the UFH pipework.  When a greater temperature is needed, they open up a valve from the ASHP/Buffer/Thermal Store (or whatever) and inject some hotter fluid into the UFH pipework, with some colder fluid redirected back to the ASHP/Buffer/Thermal Store (or whatever).

Then, when it is up to to the desired temperature, they close again and the UFH pipework is allowed to have fluid flow though it until the temperature drops and another injection is needed.

So as long as the ASHP/Buffer/Thermal Store (or whatever) is at a greater temperature i.e. 40°C for a floor flow temperature of say 35°C, then the mixer valve does the fine control. If cooling then it is reversed with warm water from the UFH pipework being sent to the ASHP/Buffer/Thermal Store (or whatever).  Actually, probably not a thermal store in this case.

 

Is that basically right?

[Jeremy Harris]

21 minutes ago, SteamyTea said:

Just so that I understand what is going one.

 

These mixer valves allow the fluid to be circulated around the UFH pipework.  When a greater temperature is needed, they open up a valve from the ASHP/Buffer/Thermal Store (or whatever) and inject some hotter fluid into the UFH pipework, with some colder fluid redirected back to the ASHP/Buffer/Thermal Store (or whatever).

Then, when it is up to to the desired temperature, they close again and the UFH pipework is allowed to have fluid flow though it until the temperature drops and another injection is needed.

So as long as the ASHP/Buffer/Thermal Store (or whatever) is at a greater temperature i.e. 40°C for a floor flow temperature of say 35°C, then the mixer valve does the fine control. If cooling then it is reversed with warm water from the UFH pipework being sent to the ASHP/Buffer/Thermal Store (or whatever).  Actually, probably not a thermal store in this case.

 

Is that basically right?

 

 

Essentially yes, but there are two types.  Ours works just like a thermostatic radiator valve.  When the sensor embedded in the upper, flow, manifold, cools below the set point, it opens the valve a bit to let a little bit of hot water in from the ASHP flow.  When the sensor is at the set temperature it closes down the valve that lets in hot water a bit.  In practice, because the response time is slow (these are capillary sensor valves with an expanding wax actuator) they work well at pretty tightly controlling the temperature as long as there is no sudden change in demand (they have a high integration time constant).  Three port valves can mix flow and return to achieve the same objective.  Two port valves allow the return to the ASHP to just pull across the UFH return manifold, mixing with the returns from the UFH that are injected into that manifold by the UFH circulating pump.

 

They all do the same thing, which is to regulate the temperature of the UFH flow to a set point.  There are some clever ways of modulating some valves, to allow the UFH set point to be changed, if required, for weather compensation.  In a low energy house this doesn't make sense, as the changes needed would require accurate 36 to 48 hours forecast data, because of the slow thermal time constant, and it happens that the system of running at a constant low temperature works very well to just self-compensate, because of the nature of the relationship between the floor surface temperature and the heat output.  Holding the floor at a near constant low temperature gives a big increase in heat output for a small decrease in room temperature, so the room will quickly heat back up to the target temperature, as long as the floor has a pretty high heat capacity and the thermal conductivity between the water in the pipes and the floor surface is good enough to maintain an adequate heat flow rate.

 

The neat thing is that such a system couldn't really care less where the heat comes from, or what the heat source flow temperature is, as long as it's around 5 to 10 deg C warmer than the UFH flow temperature.  It will work just the same connected to a boiler at 65 deg C flow as it will to an ASHP at 40 deg C.

Edited December 6, 2017 by JSHarris