NSS

Panasonic Air Rads - be warned

Recommended Posts

11 minutes ago, PeterW said:

I’m not sure even that LLH is correct as it’s behind the 3 way valve and there are what looks like tee’d returns into the manifold return before that. 

 

If that’s the case then that air rad is probably not going to get anything like the flow it needs as it’s reliant on back pressure elsewhere in the system to force the flow into it which the LLH is designed to eliminate ...

 

Also if the rad is tee’d off before the diverted valve, then it will get heat during the DHW cycle too..!

The only tee between the diverter valve and the LLH is the one that feeds the air rad.

Edited by NSS

Share this post


Link to post
Share on other sites

 

53 minutes ago, NSS said:

Okay, as most of you will have guessed, a lot of this is going straight over my head. .................

 

 

 

I can try and bring a bit of clarity, that may or may not help.

 

The low loss header was invented to overcome a problem with high temperature boilers, where if all the demand side loads closed down or reduced their flow rate below the minimum allowable flow through the boiler, there needed to be a way to have a "short circuit" between the flow and return, to make sure that the flow rate through the boiler was above the minimum required.  A lot of this was related to the need to keep water circulating after the boiler had shut down, so the boiler heat exchanger could cool slowly during the over-run period.

 

The same applies to heat pumps, but for a different reason.  They don't need the flow rate to be maintained at the minimum level during over-run, as with a modulating heat pump that can run down to a very much lower power output than a boiler there is no real need for an over run and the temperatures are so much lower that getting rid of residual heat isn't really a problem.  There is a problem at start up, though, where the heat pump needs to be sure that there is enough flow through the demand side to be able to start pumping heat.  They do this by sensing the pressure in the flow line - too high a pressure implies too little flow, and so often an over-pressure event will be triggered, shutting the heat pump down for a time.

 

The most common reason for seeing a high pressure in the flow at start up with a heat pump system, is the time taken for thermal actuators to open.  These can take several minutes to operate, and until they open the heat pump will see too high a pressure every time it tries to start.

 

As low loss headers had been used as one way around this problem with boilers, some used them on heat pumps.  This is where the first problem comes in.  All a low loss header is is a bit of vertical large bore pipe, with two flow connections opposite each other at the top and two return connections opposite each other at the bottom.  They also usually have a drain valve at the base and an air vent at the top.  They work because the incoming flow from the boiler (remember the unit you have is a 40kW boiler unit, that will be expecting water at around 60 deg C, although it will work down to about 40 deg C OK, apparently, as long as the differential between flow and return is high enough) is so hot that if there is no flow restriction on the demand side, such as closed valves or actuators, the hot water will just flow across the cooler water in the bottom and out the demand side flow connection.  Likewise, the cooler return water will come in at the bottom, and being much cooler will just shoot across the bottom and back to the heat source.

 

If the demand side is restricted (partially closed valves etc) then the flow from the heat source will turn 90 deg run down the LLH and back to the return, with very little resistance to flow (which is the "low loss" bit).  This neatly overcomes the problem of a device needing a minimum flow rate to work, with no moving parts.

 

However, it does need the flow and return temperature differential to be high enough to allow the "hot" flow water to shoot straight across when working normally, and not start mixing with the almost as warm return water coming in the bottom.  Generally they need to see around a 10 deg temperature difference between flow and return to work well, but will just about work down to around 5 deg C difference, with a fair bit of flow mixing.  Once the flow and return temperature difference drops below about 5 deg C the thing will really stop working well, and will just mix the two flows.

 

You can use these things with a reasonably high temperature ASHP OK, as long as the differential between flow and return is high enough.  I found, through experience, that the difference between the flow and return on our low temperature UFH (around 25 to 26 deg C flow) didn't give anywhere near a big enough temperature difference for a standard LLH to work.  I did find a company that made a special heat pump version, which was quite a bit taller and I think included some internal baffles, that would work OK at a 5 deg C differential, but it was expensive and would have been awkward to fit.

 

Instead I got around the problem of the heat pump needing to see a low flow resistance at start up (and it's only at start up where there is a problem, really, unlike a boiler system) by fitting a pressure operated bypass valve between the heat pump flow and return.  This is adjustable, and is set so that it only opens when the pressure in the heat pump flow line is close to the pressure where the pump high pressure event trigger operates.  This allows the heat pump to be turned on when everything else is turned on, and it then just circulates around through the pressure bypass until such time as the thermally actuated valves have opened.  As soon as these open, the resistance in the flow line reduces, the pressure decreases and the pressure bypass valve closes, allowing the heat pump to operate at full capacity if needed.

 

In practice, in heating mode the pressure bypass never operates on our system, as there is a 70 litre buffer tank that has virtually no restriction to flow.  It's only in cooling mode, when the valve to the buffer tank is closed, that the heat pump can start up whilst the UFH thermal actuators are taking their time to open.  I've recently speeded this up by replacing the main thermally actuated valve that is in the return from the UFH manifold with a newer type that uses a motor and gearbox to operate, and this is very much faster, a few tens of seconds, rather than maybe 6 minutes or so.

 

Not sure this rambling diatribe helps, but I do remember how hard it was to try and get my head around what all the various bits in a system really did in practice, rather than what the adverts said they did!

Edited by JSHarris
  • Like 1

Share this post


Link to post
Share on other sites
34 minutes ago, JSHarris said:

Not sure this rambling diatribe helps, but I do remember how hard it was to try and get my head around what all the various bits in a system really did in practice, rather than what the adverts said they did!

Not sure I need to understand what it all does, or doesn't, do, just what would be the simplest way of putting it right (preferably without it costing too much more!). The UFH seems to work well enough, with flow rates on the manifold valves balanced as per (or close to) the design values, and floor surface temperatures when zones are on peaking evenly around 25C ish. 

 

My main concern is getting good flow at an appropriate temperature to the air rad. The installer has suggested to Panasonic that we move the feed from the current tee position to between the circulating pump and the manifold, but presumably we'd need to have a valve (perhaps the currently unused 2-port one) downstream of that tee so as not to be circulating water through the air rad unless there is demand.

 

Anyone got a view on this?

Share this post


Link to post
Share on other sites

Given your UFH works well with the low temperature, and you're happy with the towel rails running at a low temperature, I think looking for a way to decouple the ASHP flow temperature from the UFH flow temperature, plus putting the air rads directly on the ASHP flow and return, seems to be the easiest fix. 

 

Doing as you suggest with a valve should fix the air rads, but it would work a great deal better if you could also get away from the need to keep the ASHP flow to such a very low level, so adding a thermostatic mixer valve to control the UFH manifold flow would seem to be a very good idea.  That then gives you the ability to run the ASHP at a warmer flow temperature whilst still running the UFH at the temperature you know works well, and the air rads should work normally on 40 deg C, with no modifications needed.

 

The only other observation I'd make is, what stops the electric heating elements in the towel rails from heating the whole of the UFH when they are both turned on?

Share this post


Link to post
Share on other sites
4 minutes ago, JSHarris said:

Given your UFH works well with the low temperature, and you're happy with the towel rails running at a low temperature, I think looking for a way to decouple the ASHP flow temperature from the UFH flow temperature, plus putting the air rads directly on the ASHP flow and return, seems to be the easiest fix. 

 

Doing as you suggest with a valve should fix the air rads, but it would work a great deal better if you could also get away from the need to keep the ASHP flow to such a very low level, so adding a thermostatic mixer valve to control the UFH manifold flow would seem to be a very good idea.  That then gives you the ability to run the ASHP at a warmer flow temperature whilst still running the UFH at the temperature you know works well, and the air rads should work normally on 40 deg C, with no modifications needed.

 

The only other observation I'd make is, what stops the electric heating elements in the towel rails from heating the whole of the UFH when they are both turned on?

Okay, thanks for that. Anyone else care to endorse this approach?

 

As for the last point, we don't have both on together. If we want to boost the towel rail temperature we simply put the UFH stat for that room into frost protection mode whilst the electric element is on and then switch it back to normal afterwards. With no circulation the towel rail warms with minimal 'leakage' into the feed and return pipework.

Share this post


Link to post
Share on other sites
51 minutes ago, NSS said:

Okay, thanks for that. Anyone else care to endorse this approach?

 

@Nickfromwales is really the expert here, so with luck he might chime in and say whether it makes sense, given what you've got, or not.

 

51 minutes ago, NSS said:

As for the last point, we don't have both on together. If we want to boost the towel rail temperature we simply put the UFH stat for that room into frost protection mode whilst the electric element is on and then switch it back to normal afterwards. With no circulation the towel rail warms with minimal 'leakage' into the feed and return pipework.

 

Makes sense, as long you don't forget to turn the towel rail heater off, or else they will end up heating the UFH!

 

I fitted our electric towel rails to a circuit with a timer, partly to reduce the time they were on, but largely because the last house we had with an electric towel rail I found we were forever forgetting to turn it off...............

Share this post


Link to post
Share on other sites
2 hours ago, NSS said:

Okay, thanks for that. Anyone else care to endorse this approach?

Apart from the glitch with thectowel rads, as highlighted, I don't see a huge overhaul being required

As Jeremy suggests, a probe / TRV thermostatic blending valve can be introduced at the manifold and that will regulate the floor loop flue temp nicely. Then you can run the ASHP heating temp just high enough to bring the air rads on by themselves. ( Modifying the rads is a step sideways not forward imo ). 

Tee off for the air rads after the LLH so your getting bigger flow ( and a better mix ) through it, and utilise the wasted 2-port ZV for control of the rads. 

 

Now can we go to the pub ?

  • Haha 1

Share this post


Link to post
Share on other sites
10 minutes ago, Nickfromwales said:

Now can we go to the pub ?

Are you buying?

Share this post


Link to post
Share on other sites

Okay, spoken to the installer and they say that a blending valve is not only unnecessary, but that heat pump manufacturers generally advise against using them.

 

I'll get my tin helmet :S

Share this post


Link to post
Share on other sites
2 minutes ago, NSS said:

Okay, spoken to the installer and they say that a blending valve is not only unnecessary, but that heat pump manufacturers generally advise against using them.

 

I'll get my tin helmet :S

First off thet should be able to INDEPENDENTLY identify the issues here and resolve them with some sense. 

1) heating flow temp is too low for the air rads 

2) air rads temp is too high for the UFH loops to accept directiy

3) LLH shifts water not heat so cannot either rule or define these temps

4) simple solution is to fit a TMV and job done

5) you could refine this by fitting a small buffer but a bypass arrangement ( e.g. your LLH ) provides this anyhoo

 🤔

Are these the same installers who fitted a 2-port after the 3-port for giggles ?

  • Like 1

Share this post


Link to post
Share on other sites

Is anyone filling to put up a couple of sketches.  One with the ideal installation for NSS's house and one that would be the absolute ideal installation for UFH, a rad or two and a towel rail with electric element.  It may make it a bit clearer to follow.

I suspect that the installers are plumbers that have decided to do a few HPs rather than experts in then (X is an unknown quantity, spurt is a drip under pressure). 

Share this post


Link to post
Share on other sites
On 07/12/2017 at 08:43, Nickfromwales said:

A 2-port AFTER the 3-port valve o.O

 

I noticed that as well.  There are lots of different perfectly valid installation approaches.  Lots of debates about the advantages and disadvantages of S vs Y plan, though for an installation of this size, I would have expected S plan.  SY plan if such a thing exists is just bizarre, and smacks as if the installer doesn't really know what he or she is doing, IMO.

 

A Y plan value in this configuration is just plain wrong, IMO.  Surely you  don't want a preference setup on this system as the boiler could drive both; this needs replaced by standard S plan.   

Share this post


Link to post
Share on other sites
14 minutes ago, TerryE said:

A Y plan value in this configuration is just plain wrong, IMO.  Surely you  don't want a preference setup on this system as the boiler could drive both; this needs replaced by standard S plan.   

There are 2 types of 3-way valve. One is a mid-position and one is a diverter. This one, following the link from the part number, is a diverter so can actually only give fliw to one port or t'other ;) For mixed / combined flow ( true Y plan where a single flow temp can serve the rads and the dhw cylinder simultaneously ) the mid-position valve is the kiddy.  

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now