Ecodan 8.5kW PUZ-WM85VAA

[athlonoc]

Hi,

 

I have two questions if that's ok.

 

1) The HW tank is set to reach 55 degrees and reheat when it drops to 45. My question being, is it normal for the heat to disappear quickly when it's not being used much? After reaching maximum temp during the early evening, I looked at the temperature in the morning and it had lost 5 degrees and we hadn't used any while we were asleep. It's currently at 50 and dropping? 

 

2) The installed system in my EPC A rated new build has noise issues. The installers have already dropped the flow rate to 14 litres a minute ( I think ). They assured me that this wouldn't inhibit efficiency. Our issue was the noise of the pumps ( 2 CH and 1 HW ) and or the noise of flow through the pipes. Turning the flow down has allowed us to sleep at night but the two bedrooms that are back to back in our home are where the water flows up the inside of the walls to the system in the loft from the ASHP. The noise there we know will prevent anyone from sleeping as its louder than we experience on the other side of the house which has been helped by turning down the flow rate. They are looking to try and sort this out but the general consensus is that this is normal. 

 

Any thoughts, ideas or known solutions would be very welcome.

 

Thanks

 

 

[Happy Valley]

We have a 8.5kW Ecodan but run our hot water cylinder to 50 degrees. Our 210 litre tank is in the utility room and probably losses 5 degrees over a 12 hour period although haven't really checked this. Even at 45 degrees the water is warm enough.

 

Initially our installers said to leave the hot water on constant so it just tops up but we have decided to run it just once a day during the day as we don't use that much. 

 

 

[TW9]

Yes, it's normal for the tank to gradually lose heat. How much it loses will depend on where it is and how well the pipework is insulated (I'm assuming it's a modern tank with built in insulation so there isn't much you can do to improve that).

 

We heat ours to 50 degrees, which is hot enough.

[joth]

2 hours ago, athlonoc said:

1) The HW tank is set to reach 55 degrees and reheat when it drops to 45. My question being, is it normal for the heat to disappear quickly when it's not being used much? After reaching maximum temp during the early evening, I looked at the temperature in the morning and it had lost 5 degrees and we hadn't used any while we were asleep. It's currently at 50 and dropping? 

Unless you have secondary return running all the time, this will mostly depend on the ErP rating of your cylinder. We got a ErP A rated specifically for this reason (Oso Geocoil 300L). It drops about 4 degrees per day, so less that half the rate yours appears to be dropping. It's spec has it rated to lose 1.18 kWh/day, so about 4p per day (assuming COP of 2 for DHW, and on Octopus Go). (Of course being indoors this offsets 1kWh of space heating in winter, so at the moment really only costing 1-2p per day due to COP difference)

 

 

 

[athlonoc]

Thanks for all the responses. I'm not sure whether my two tanks ( not including expansion vessel )are top rated tanks. The smaller ( 50L ) of the two is B rated see picture label small tank and the other larger 250L tank see picture large tank.

It was installed in December 2022. The pipes are all covered and buried in 400mm loft insulation. The tanks just sit above it all on a raised platform.

 

So it appears all is as expected and the temperature loss is normal.

 

Any thoughts about the noise issues?

 

[ReedRichards]

5 hours ago, athlonoc said:

The pipes are all covered and buried in 400mm loft insulation. The tanks just sit above it all on a raised platform.

 

 

Unfortunately this means that your tanks are outside the heated fabric of the building.  So they are exposed to cold air and the heat they lose is wasted.  You can buy high tog duvets fairly cheaply, I wonder if it would be worth sewing one or two together to make an insulated cover for your tanks?

 

15 hours ago, athlonoc said:

Our issue was the noise of the pumps ( 2 CH and 1 HW ) and or the noise of flow through the pipes. 

 

I have this issue with my heat pump system, although it's not nearly as bad as in your case.  Heat pumps typically target a small temperature differential around the heating system so that requires much higher flow rates than you would use with a gas or an oil boiler.  If you reduce the flow rate it will make your heat emitters less efficient but It would not necessarily reduce the overall efficiency (I think).  In my case I'm not sure if the noise originates from the pump and is carried along the pipes or if it really is flow noise.  Could you try filling your wall with sound-proofing insulation, if you have not already done so?          

[joth]

The 50L cylinder is the buffer tank, so not relevant for your DHW temperature loss but adding equivalent losses to the heating circuit.

https://www.cordivari.com/Calorifiers/Inertial_tanks/volano_termico_pdc_hanging

 

The pumps are all in the loft? They're naturally going be much more audible there. We have some heating pipes in our loft (warm loft, so minimal insulation from bedrooms) are they're silent when running, as the pumps are far away in the corner of plant room downstairs.

 

[TerryE]

On 31/01/2023 at 08:18, athlonoc said:

is it normal for the heat to disappear quickly when it's not being used much?

Depends on the type and how well insulated your tank is.  We use SunAmps which have vacuum panel insulation and these stay hot for days.

[HarryUp]

Mitsubishi spec is that the tank heat loss for a 250l tank is 1.5kWh per 24hrs, which equates to about 5 or 6 degrees of water temperature. And that is possibly just measuring the tank, with all the heat conducting copper attached it will be greater. Mine has still lost about 10 or 12 degrees by the time the next HW cycle starts if there has not been a major water draw such as a shower. But I do wonder if the water sitting above the pocket where the thermistor is situated remains more usefully hot whilst the cooling water is also sinking down the tank – even when the reported temperature is tepid the delivered water seems to remain showerworthy hot. If your tank is in an unheated area you should ensure the pipes that enter the tank are as best insulated as you can. I found that after a hot water cycle even the cold water inlet pipe was noticabley warm. And particularly the pipework that forms the hot water heating loop. I had to do it myself as my installers only lagged the easy straighter runs, and it was rather fiddly.

 

I did read somewhere that one installer did not specify Mitsubishi tanks as they had noisy pumps. And this is certainly my experience. Having been concerned beforehand about potential noise from the external unit, I find any noise from that quite bearable as it is mostly a low pitch moving of air. However, one or other, or both, of the circulation and CH pumps fitted to the tank really annoy me. It isn't so much volume as they don't seem too loud even standing right in front of them, but the quality of tone and pitch I find mildly unpleasant and the sound just seems to carry through the walls easily. I haven't really explored implementing a solution yet (sorry!) but I am thinking of trying to get some sound-deadening foam and loosely boxing each pump in.

[athlonoc]

On 04/02/2023 at 23:28, HarryUp said:

Mitsubishi spec is that the tank heat loss for a 250l tank is 1.5kWh per 24hrs, which equates to about 5 or 6 degrees of water temperature. And that is possibly just measuring the tank, with all the heat conducting copper attached it will be greater. Mine has still lost about 10 or 12 degrees by the time the next HW cycle starts if there has not been a major water draw such as a shower. But I do wonder if the water sitting above the pocket where the thermistor is situated remains more usefully hot whilst the cooling water is also sinking down the tank – even when the reported temperature is tepid the delivered water seems to remain showerworthy hot. If your tank is in an unheated area you should ensure the pipes that enter the tank are as best insulated as you can. I found that after a hot water cycle even the cold water inlet pipe was noticabley warm. And particularly the pipework that forms the hot water heating loop. I had to do it myself as my installers only lagged the easy straighter runs, and it was rather fiddly.

 

I did read somewhere that one installer did not specify Mitsubishi tanks as they had noisy pumps. And this is certainly my experience. Having been concerned beforehand about potential noise from the external unit, I find any noise from that quite bearable as it is mostly a low pitch moving of air. However, one or other, or both, of the circulation and CH pumps fitted to the tank really annoy me. It isn't so much volume as they don't seem too loud even standing right in front of them, but the quality of tone and pitch I find mildly unpleasant and the sound just seems to carry through the walls easily. I haven't really explored implementing a solution yet (sorry!) but I am thinking of trying to get some sound-deadening foam and loosely boxing each pump in.

Thanks for supplying this information. Its good to know that there is this amount of expected heat loss on a modern tank. I might endevour to do the same with lagging every inch of pipe to see if it makes any difference. Has anyone tried wrapping the tank further in a thermal blanket? Is there much point if they did?

 

The noise is as a point where the installer said all adjustments that can be made have been made. The flow rate is now down to 9 litres a minute and its now at the bottom end of the tolerance to accept its efficiency isn't compromised. 

Seems we will have to live with the noise which is disappointing.

 

Thank you all for your thoughts, knowledge and comments.

[SteamyTea]

On 01/02/2023 at 12:48, TerryE said:

We use SunAmps which have vacuum panel insulation and these stay hot for days.

Not the only reason. The phase change is the main reason it can stay usable for a few days. 

As a rule of thumb, 20mm of vacuum panel is about the same as 100mm of PU foam (give or take).

I have only looked inside 1, early SA and seem to remember that the VP was not very thick, and poorly fitted.

 

Very easy to add extra insulation around a cylinder, it reduces losses even when the thickness varies i.e. round cylinder in square cupboard, just stuff wool into the corners.

 

You can also reduces the mean store temperature if you reduce losses and have the same usable amount of DHW.