Advice needed before I tackle the installers!

[MattB67]

I'm having a number of problems with a shiney new Daikin Altherma 3 installed in September (COP down at 2.5 already with intended SCOP of 3.7; radiators cold at the bottom hot at the top; system pressure keeps dropping). I've emailed the installers a couple of times and got no reply, so this week I'm going to start phoning them up. So I don't get fobbed off I'd appreciate some advice on three things.

 

1. There's a red expansion vessel, and a white Zilmet VSG Solar temperature reducing vessel (pictured). It looks like all the CH and HW is passing through the Zilmet. It is in the loft and permanently warm so I was thinking I should insulate it. From reading up it looks like this is designed to limit the heat from solar thermal, which can be as hot as 90C. But I don't have solar thermal and no intention of getting it. I have CH running at 45C and hot water around 50C, once a week 60C for the legionaries program. So isn't this thing just wasting heat as it's in the loft, not living space? Is the effect any different from leaving some pipes without lagging or could it actually have a useful purpose? Rather than me insulating it I think they should just take it out.

 

2. Part of the install was a brand new 125L indirect HW cylinder. From the max temp of 54C, it will drop to 44C within 24 hours, even if I avoid turning on any hot water taps all day. Is that heat loss normal? I thought modern cylinders were only supposed to lose 1-2% heat per day?

 

3. I have had to refill fill the system several times, because pressure drops from 1 bar to 0.2 bar within a week. I can't find any leaks from the radiators or pipework. So I guess the pressure dropping might be an expansion vessel problem? 

One thing I don't need guidance on though is whether they've put the unit too close to the walls. The Daikin installation manual says this outdoor unit should have at least 250mm clear at the back and side. It's been installed with 140mm and 160mm, so I am going to insist they move it, and will complain through MCS if they refuse. Lack of airflow has got to be contributing to poor COP.

 

Thanks for thoughts on the above.
 

[Marvin]

It's very difficult to jump in when you don't know all the history ...

 

In my humble opinion....

 

Item 0: if radiators cold at top and hot at bottom means top full of air  if radiators cold at bottom and hot at top heat coming out of radiator quicker than the hot water is replacing the cold water. Possibly a pump issue but water flow not travelling fast enough.

 

Item 1: don't know about Zilmets but all in loft? I would insulate the pipes as thick as possible and all other items I could.

 

Item 2: our 215 litre indirect tank can loose the same amount of temp in a day, but we are working on insulating it more. We have it in our bungalow in the utility room.

 

Item 3: the expansion vessel is not leaking otherwise there would be a puddle on the floor. You have a leak or the air in the system is still draining out.

 

Last item:  Sorry to hear of the positioning.  The further away the better.

 

Good luck

 

Marvin

 

Edited November 7, 2021 by Marvin
Info on pump

[MattB67]

2 hours ago, Marvin said:

It's very difficult to jump in when you don't know all the history ...

 

In my humble opinion....

 

Item 0: if radiators cold at top and hot at bottom means top full of air  if radiators cold at bottom and hot at top heat coming out of radiator quicker than the hot water is replacing the cold water. Possibly a pump issue but water flow not travelling fast enough.

 

Item 1: don't know about Zilmets but all in loft? I would insulate the pipes as thick as possible and all other items I could.

 

Item 2: our 215 litre indirect tank can loose the same amount of temp in a day, but we are working on insulating it more. We have it in our bungalow in the utility room.

 

Item 3: the expansion vessel is not leaking otherwise there would be a puddle on the floor. You have a leak or the air in the system is still draining out.

 

Last item:  Sorry to hear of the positioning.  The further away the better.

 

Good luck

 

Marvin

 

Thanks for the advice. Yes it's not ideal that it's all in the loft, but I think the heat loss can be reduced a bit more. I have bought 25mm wall pipe lagging to replace the 9-13mm they fitted because the lagging feels slightly warm to the touch. I'm going to tape seams and joins as well. But it seems a bit pointless if there's an uninsulated white metal vessel that is there to let heat out of the system.

 

Interesting that there could still be air trapped. There was a problem with the 3 way valve they sorted out a few weeks ago - it was putting the HW into the CH circuit. I did wonder if they did an air purge afterwards. I can't find any leaks in the pipework and but there are a few floorboards I still need to pull up. I've bled the radiators a few times and refilled, and there doesn't seem to be any more air in the rads. But I guess air could be anywhere in the circuit. It's possible to make the unit do an air purge, but you have to go through installer settings, so I'm waiting to clear that with the installers in case something goes wrong.

 

Could an expansion vessel that just needs recharging with air cause a pressure drop like that? 

[Marvin]

1 hour ago, MattB67 said:

Could an expansion vessel that just needs recharging with air cause a pressure drop like that? 

Well,  the limit to the expansion vessel pressure drop is the volume of the red expansion tank. Another possibility is the pressure relief valve is letting some water out.

 

Good luck.

[J1mbo]

Do you know the approx volume of water in the system?

 

The DHW tank dropping could be the diverter valve passing, so that the system is drawing heat from the cylinder.

 

The system pressure dropping is a leak. The expansion vessel looks like maybe 18 litre which should be easily enough for 250 litres at these flow temperatures provided it's pre-charge has been set correctly. If it's too small the system pressure will rise dramatically as the system is heated.

 

The uneven radiator temperatures is insufficient flow. Increase pump speed and ensure both valves of affected radiators are fully open. Note than it's normal for the centre of large panel radiators to feel somewhat cooler.

 

What controls are you using? Anything introducing short-cycling or limiting the volume of water circulating will dramatically impact performance.

[MattB67]

3 hours ago, J1mbo said:

Do you know the approx volume of water in the system?

 

The DHW tank dropping could be the diverter valve passing, so that the system is drawing heat from the cylinder.

 

The system pressure dropping is a leak. The expansion vessel looks like maybe 18 litre which should be easily enough for 250 litres at these flow temperatures provided it's pre-charge has been set correctly. If it's too small the system pressure will rise dramatically as the system is heated.

 

The uneven radiator temperatures is insufficient flow. Increase pump speed and ensure both valves of affected radiators are fully open. Note than it's normal for the centre of large panel radiators to feel somewhat cooler.

 

What controls are you using? Anything introducing short-cycling or limiting the volume of water circulating will dramatically impact performance.

Thanks J1mbo.

 

Yes, I wondered if the diverter valve might be causing problems still (they called it a 3 way port, I'm guessing that's the same thing?). They did come out and fix one problem with that, but maybe it's still not right.

 

I don't know the volume of the system. It's a smallish 3 bed Victorian mid terrace with about 9kWh worth of radiators (at Delta 50). The radiator that's most affected is in the dining room, right at the end of the CH circuit. The downstairs is quite a bit colder so I've got the downstairs radiators open full flow at both ends, and limited the upstairs ones as upstairs has been getting too warm.

 

The system is controlled by a Hive thermostat downstairs, which I guess is just sending 'on' or 'off' signal to the Daikin indoor unit, and then that decides how to deliver the heat. The outdoor unit seems to be running more or less constantly, and is an inverter so hopefully won't cycle too too much. When you say 'anything limiting the volume circulating' - would that be reduced by having the pump run a bit faster? 

 

Edited November 8, 2021 by MattB67

[J1mbo]

Does the Hive specifically have a configuration for ASHP? I would suspect this is the main problem. I would suggest standard TRVs upstairs and valves fully open downstairs. Whatever control you have make sure that weather and room temperature modulation are enabled. Any control with a TPI algorithm will mess up the heat pump.

 

To balance the system, close the lock-shield valves of all the radiators that are fully warm half a turn and see how that goes, and repeat.

Edited November 8, 2021 by J1mbo

[MattB67]

Just now, J1mbo said:

Does the Hive specifically have a configuration for ASHP? I would suspect this is the main problem. I would suggest standard TRVs upstairs and valves fully open downstairs. Whatever control you have make sure that weather and room temperature modulation are enabled. Any control with a TPI algorithm will mess up the heat pump.

Hmm. I don't think so. It's a standard Hive thermostat. I thought all the Hive is doing is replacing the thermostat on the indoor unit, because that's in the loft. There are menu options for editing the curves etc on the indoor unit, including weather dependent curves (not currently enabled). I was assuming the Hive is setting a target temperature, then the indoor unit decides how best to meet it. But maybe that's another cause of the problems. 

 

Overnight I have the Hive set to 18C, during the day I turn it to 20C. Depending on the ambient temp it could take 4-5 hours to get to 20C downstairs, if at all. I was thinking that would be a product of heat losses in the loft and the dining room radiator being cold at the bottom - plus the poor location of the inverter making the system work harder. For that morning warm-up, assuming the indoor unit is using a reasonable curve, I'm wondering if the Hive would have much effect on that? 

[J1mbo]

So is the system set to a fixed flow temperature of 45°C then? And simple on-off switching?

[J1mbo]

To add, if you have Hive TRVs on the cooler radiators, take them off. I have seen a couple of electronic TRVs that fail to open valves properly.

[MattB67]

2 hours ago, J1mbo said:

To add, if you have Hive TRVs on the cooler radiators, take them off. I have seen a couple of electronic TRVs that fail to open valves properly.

Luckily not, no. Just standard TRVs.

 

4 hours ago, J1mbo said:

So is the system set to a fixed flow temperature of 45°C then? And simple on-off switching?

I think that's what it must be doing. I was misunderstanding 'curves'. I thought they were how the unit heats up the water over time to save power. Looking at the options in the system it looks like a curve is about setting the flow temp according to the outside temp? Weather dependent curves aren't enabled, it's in 'setpoint mode', so yes I guess it keeps running at 45C until it reaches desired temp. 

 

I was assuming the Hive thermostat was a bit more sophisticated than being an on/off switch. I was expecting it to send at least two signals to the indoor unit, to tell it the desired temp and the actual temp, and let the heat pump work out how it gets there. But maybe not. I could enable WD curves. The only problem is that the system was designed for 20C internal, 45C flow at -3C outside. But because the house has been struggling to get to 20C even when it's 10C outside, because radiators aren't heating up properly and there's some waste in the system, there isn't much room for weather dependent curve to use a lower flow temp. But once the other issues have been addressed, (heat pump location, flow speed, lagging etc), that could be something to look at.

[MattB67]

Time for an update here, as I've managed to sort out all the issues I was having with the Daikin Altherma 3.  Shortly after installation I was getting a COP of 2.5 in a mild autumn. I managed to get this to 2.7 by being more careful with target temperature, etc but still way below the target scop of 3.7.

• The dining room radiator that was cold at the bottom was clogged with sludge. I took it off the wall, emptied and hosed it out. There was a lot of thick black water and it probably collected in that radiator because of its shape, being a column radiator, and is the last rad on the circuit.  I think the installers should have done a powerflush, but at least now it's sorted.
• The installers said this about the Zilmet vessel, ""We have installed a Volumiser vessel which provides additional water volume to the central heating system, this is required when the system goes into de-frost."  They offered to lag it, but I just went ahead and did that as I had some leftover from lagging the water tank. See pic below.
• Also I replaced heating circuit pipe lagging in the loft with all 25mm wall, instead of the standard 9mm they had fitted. 9mm pipe lagging makes a huge difference compared to bare pipes, but using this calculator https://kalk.pro/en/heating/pipeline-heat-loss-calculator/ I realised it would be worth upgrading to 25mm. It cost about £50 to buy but I reckon I'll reduce heat loss by 3kwh a day. If that's 1kwh consumption, that's about £6-7 a month saved, so it pays for itself pretty quickly.
• Still no idea why the DHW cylinder loses heat so quickly. That hasn't changed.
• I finally found the leak! After checking nearly all pipes, I noticed the copper below the lockshield valve in the bathroom was a bit stained. There was no feeling of damp, but I cleaned up the copper and tightened the lockshield, and finally the pressure stabilised. Luckily I didn't have to resort to Roger of SkillBuilder's YouTube suggestion - putting poundland purfume in the system and waiting  a few days until one room "...smell's like a Tart's boudoir!" (that's a quote)
• After much badgering I finally got the installers to agree to move the condenser unit in mid December, so it's now 300mm from the back wall and 250mm from the side. However they did also say they've found Daikin send out the condensers pre-charged with refrigerant, but haven't been putting enough in. So he weighed the gas out at 1.35kg, but put back in 1.6kg. Both these things would have been contributing to low COP, so in a way I'm lucky they put it in the wrong place and had to empty out the unit anyway, because if the cop had been a little bit better I might not have persisted in getting it moved. After this fix the COP improved 25% overnight.
• One other important point was I miscalculated radiator capacity downstairs. I basically increased capacity x 1.5 throughout the house, but I'd forgotten that the open plan lounge/diner/kitchen was always a bit cold, which I used to overcome by turning the gas boiler up, and the upstairs radiators down. When I checked the heat loss calculations it was clear I needed more capacity, so changed one rad from a type 21 2.2kwh to a type 22 3.2kwh, and that's made it much easier to keep downstairs warm.

With all these fixes the cop is probably now around 3.3ish. I'm now testing dropping the flow to 40c to see what's the lowest flow temp that will keep the downstairs warm. I'm also trying out a thing called a Speed Comfort, which is a bit noisy, but I think a good idea - it's basically 3 computer fans in a block with magnetic catches, and a thermostatic switch. You put it at the bottom of the radiator and it blows air up through the convectors to distribute heat into the room better. I've only got one on a 1800mm rad, (they say you need three) and it was £55, but I think it might prove to be worth the money because so far the room feels warmer and heats up more quickly, even at this lower flow temp. I'll reserve judgement for now, and we had a lot of very mild weather so I won't know how good the cop and consumption is until we've had some cold weather to compare.

 

Before the fixes listed the system was using 16-17kwh daily average. In similar weather I reckon that's more like 10-11kwh now, so a huge improvement. 

 

Thanks again for all the advice given, and happy new year to you all. 

 

 

Edited January 2, 2022 by MattB67

[ProDave]

Thanks for the update, it looks like you found some real issues that are now resolved.

[MattB67]

5 minutes ago, ProDave said:

Thanks for the update, it looks like you found some real issues that are now resolved.

Yep, and I've given a lot of detail there, but hopefully it might be useful to someone in future. 

[Gus Potter]

@MattB67

 

Glad you got it sorted!

 

I'm old sckoooool but the old plumbing / hydraulic rules still apply even with modern unvented sytems./ ASHP etc. 

 

It looks great having all the pipes level and well clipped, nice to see on an electrical system but on plumbing no. We know we need to get the air out so lets run the pipes on a slope so we can get the air to a place we can easily vent it. Don't do your smaller bore (any pipes if you can) pipes so air, debris can get trapped.. no funny U bends just under the rads say.. run them so that the metal gunk gets picked up by the magnetic filter. Make it easy to flush out the stuff that the magnetic filter won't catch.. it basic stuff and good workmanship.

 

If you are using under floor software to design your loops make sure you check you bend radius is compatible with the pipe you are using! And when you are installing pay particular attentions to the bend radius or you are inviting trouble. Worry less about the pipe spacing as if you choke a loop you will have much more to worry about!

 

If you take care of the basics you'll save yourself a lot of grief later and get the best out of your tecky controls. Take care of the basics and this will allow you to get value out of your high tech controls.

 

For me I would go for the simplest design that you can that is easily maintained by your local heating Enginner. Save your money.. and spend it on insulation or making your house just a great home.. buy some furniture, pots pans etc.

 

 

 

 

[SteamyTea]

11 hours ago, MattB67 said:

Speed Comfort

Sounds magic, would like to know how putting in less energy gets a room to the same temperature.

Lower heating costs

SpeedComfort helps contribute to significantly save money on your energy bills. This is because of several smart properties:

• The SpeedComfort results in a lower supply temperature of the central heating water, which saves gas
• A lower temperature of the central heating water means less heat loss in pipes
• Thanks to the SpeedComfort, the room is brought to temperature faster, meaning the boiler is not running for so long.
• Adjustment on the water side of the installation yields further savings

[ReedRichards]

You can buy radiators with an integral fan but the point of the fan is that it increases the heat output from the radiator.  That means your heat pump/boiler has to supply more energy to the radiator so a fan will increase your energy bill if it does its job.

 

Radiators with integral fans are useful in situations where you don't have room for a bigger radiator without a fan.  But on some of the ones I have seen, the fan only cuts in when the water temperature gets high enough and an ASHP may not get your water to the cut-in temperature.  

[joth]

4 hours ago, SteamyTea said:

Sounds magic, would like to know how putting in less energy gets a room to the same temperature.

 

 

They don't actually say that. They say allows lower temperature to be put into the heating circuit. In many houses (I'd almost wager the majority, certainly, the majority where CH was a retrofit) a lot of pipework is uninsulated and travels in cold voids outside the useful thermal envelope of the building (e.g. under floor voids or in the loft). By extracting more heat in the room (i.e. increasing delta T across the radiator itself) it will reduce the average temperature in the circulation pipes (esp the return pipe, but potentially also the supply pipe if the whole system can now run a bit lower) thereby reducing the wastage from the pipework blowing out the building in useless locations.

 

Put simply, if you can improve the ratio of energy delivered to room vs energy wasted in the pipes, then getting the same amount delivered to the room will require less total output from the boiler.

 

that is all irrelevant to a well designed system in a low energy house where "wastage" in the pipework is still in the thermal envelope so not wasted at all.

 

[SteamyTea]

11 minutes ago, joth said:

all irrelevant to a well designed system in a low energy house where "wastage" in the pipework is still in the thermal envelope so not wasted at all.

Yes, and it is still best to insulate what you can, even when I side the heated envelope.

 

In my old house, there was a ceiling fan, that was quite good at forcing some of the higher than mean temperature air downwards.

[MattB67]

I'm reserving judgement about the Speed Comfort for now, because temperatures have been in the double figures for a while here in Bristol.

 

The reason I decided to give it a go is that downstairs I have 3.2kwh rad behind the sofa and 1.4kwh rad at the dining room end, and the other way to get the flow temp lower would be to fit a triple radiator and lose even more space. The sofa is very close to the radiator, so I think this is helping get more heat out into the room, instead of just warming up the sofa itself. The room definitely warms faster, and this is with flow at 40C instead of 43-45C I was using before. So although it might require the ASHP to deliver slightly more heat overall, that should be at a better COP because I've been able to drop the flow temp. Anyway, we'll see....

 

8 hours ago, ReedRichards said:

Radiators with integral fans are useful in situations where you don't have room for a bigger radiator without a fan.  But on some of the ones I have seen, the fan only cuts in when the water temperature gets high enough and an ASHP may not get your water to the cut-in temperature.  

 

I wondered about that but at 40C flow it's switching on and off when I'd expect. It comes on after the heat pump has been running for 15 mins. Probably at lower flow temperatures it would hardly ever be on, so not suitable for all ASHP setups.

 

The main problem is the noise, it's as noisy as an old skool pc fan. It's made of two pieces of plastic clipped together which vibrate, so I've put bolts through which has helped. But also the whirring is exaggerated by being in contact with the radiator, so today I've put it on some bits of wood instead of fixing it to the radiator with the magnetic clips. Also I wondered if it might be annoying having it blast air up the back of my neck when I'm watching TV. In fact the airflow is not all that noticeable.

 

Edited January 3, 2022 by MattB67

[SteamyTea]

24 minutes ago, MattB67 said:

1.4kwh

 

24 minutes ago, MattB67 said:

3.2kwh

No you haven't.

kWh is energy, kW is power.

[J1mbo]

@MattB67 aluminium radiators might be worth a look, I’ve had great success with Faral Tropical 95s. They are though very expensive,

Edited January 4, 2022 by J1mbo

[SteamyTea]

12 minutes ago, J1mbo said:

aluminium radiators

I have often wondered if there is a real benefit from using aluminium.

Depending on grade of aluminium and the steel, you may get almost 5 times more heat transfer, trouble is, the temperature differences are relatively small, and they are in effect, in a steady state.

Aluminium has a k = 230 W.m^-1.K^-1

Steel k = 50 W.m^-1.K^-1

I don't know what thickness the material will be but a steel radiator is probably thinner than an aluminium one.

This is only half the story though.  When a radiator is cold, it takes energy to heat it up.

Aluminium has a SHC of 0.921 kJ.kg^-1.K^-1

Steel is 0.502  kJ.kg^-1.K^-1

But the water that is pumped around takes 4.2  kJ.kg^-1.K^-1

I think the thermal properties of the water will tend to swamp any advantages that the radiator material will make in reality.

It would be nice to see a proper study on this as there may be marginal cases where an aluminium radiator does have an advantage i.e. small radiator heating a small volume.

I suspect that there is a greater advantage to the manufacture than the user.  Aluminium is easily extruded, so more interesting designs can be created quite cheaply.  Nothing wrong with that, but it would be good to see some genuine like for like comparisions.

[J1mbo]

57 minutes ago, SteamyTea said:

I have often wondered if there is a real benefit from using aluminium...I think the thermal properties of the water will tend to swamp any advantages that the radiator material will make in reality.

 

Agree. The aluminium Tropical95's (and their numerous copies) simply have oodles of surface area.

 

The datasheet gives the output at all flow temperatures from dT=20 to dT=79: https://www.warmrooms.co.uk/Controls/List/Download.ashx?ListItemId=22198&File=1

Edited January 4, 2022 by J1mbo

[Temp]

On 02/01/2022 at 22:10, MattB67 said:

The dining room radiator that was cold at the bottom was clogged with sludge. I took it off the wall, emptied and hosed it out. There was a lot of thick black water and it probably collected in that radiator because of its shape, being a column radiator, and is the last rad on the circuit.  I think the installers should have done a powerflush, but at least now it's sorted.

 

If that was mine I'd drain and refill system several times and make sure there was the right concentration of corrosion inhibitor in it.