ASHP and insufficient hot water

[sinaloa]

Hi Si H, I am hoping that when the cavity insulation is done I'll have enough spare capacity to heat the water twice a day rather that once a day. That would be sufficient for our hot water needs.

I note that the Ecodan usually comes as a package with a cylinder with a bottom mounted element. Ours didn't but perhaps I'll have to resort to this.

You mention the weekly sterilising under MCS 3005 but I presume this won't be possible unless our immersion heater has an element at the bottom of the cylinder ot have a de-strat pump as any other arrangement will not be able to heat the whole of the tank to the required temperature?

I'll try to post the picture you requested later.

 

[Nostrum]

It's something I've often thought is inevitable. There is always the 'what if' when using the historic data to calculate the design temp for a system. If you design it at -10 in a few years times its not impossible for us to witness temperatures below this, is it?

To an end user like yourself, you pay your money and expect to be warm all year round, not much to ask. As we all know though an average isn't going to allow for the coldest days and this is why I always tell the customer how the calculation works.

For 99% of the year the heating system is probably perfectly sized, but that 1% could be cause for complaint. The mcs guidelines state that the heat pump must be sized to provide 100% of the heating and hot water requirements excluding supplementary heating/immersions. However it also gives guidelines on calculating heat loss using the historical data.
technically, yes the heat pump is obviously undersized as you are not ale to extract enough heat to heat both, but theoretically the heat pump sounds from what you have said to have been correctly specified and in compliance. So who's to blame?

We are in a position whereby efficiency is becoming a big agenda and by sailing too close to the wind as it were in order to achieve maximum efficiency may lead to a shortfall, especially for heat pumps as the outside temperature directly relates to the output of the unit as well as the heat loss through the fabric of the building.

 

[Nostrum]

Also, Unfortunately manufacturers, mcs and decc have to show that the figures are adding up on paper to make it all worthwhile, regardless of the real world scenario. That said, your better off with a shortfall for 2 weeks of the year than an oversized heat pump that is costing you more to run all year round.

Ive no experience with the ecodan but the daikins units control the pasteurisation cycle themselves if I remember.

Also, you can actually get bigger immersions than 27" , 30 & 36 are available.

 

[lame plumber]

this whole issue just proves to me that just because someone sits more exams and gets the boxes ticked, doesnt mean to say they know what they are doing and a customer suffers. theres to much pushing for ticking the boxes and getting mcs accredited in order to be able to offer customers rebates and not enough doing a decent job out there. I personally would not have installed a system in a property that is not correctly insulated in the first place, even if it was going to be done later as it wont work, as seen. Bringing an old property upto modern standards of insulation is more difficult than most folks realise

 

[sinaloa]

Thanks again Chris. If the cavity wall allows me to divert ASHP for an hour or so during the day from space heating to give the water a boost we would have enough hot water. That would just leave me with the problem of the recommended weekly boost to avoid the dangers of legionaires with an immersion.

PS Looks like I'm going to get a lot of consultancy fees to pay - serves me right I suppose !!! LOL

 

[chris watkins]

Thanks again Chris. If the cavity wall allows me to divert ASHP for an hour or so during the day from space heating to give the water a boost we would have enough hot water. That would just leave me with the problem of the recommended weekly boost to avoid the dangers of legionaires with an immersion.

PS Looks like I'm going to get a lot of consultancy fees to pay - serves me right I suppose !!! LOL

It is worth just trying to see if one whole cylinder full of hot water, at a good temperature, will do you for the whole day ? un-less you are a very large house with lots of bathrooms then 245 L should. This would at least give you the option of not having to loose the heating during the day.

All this is of course trying to correct not an idea installation but there are still lots of details which we are not party to regarding the design or the installer (it may well be that the customer was made aware of the limitation of the system without the correct insulation levels or not, before the installation) etc.

I have not done any of these systems (air or ground) but try to keep up to date one thing that interests me is "

The mcs guidelines state that the heat pump must be sized to provide 100% of the heating and hot water requirements excluding supplementary heating/immersions" is this true sambotc ? not doubting you cos I know you have done some of this but it does seem a bit much given the limitation of these temp wise.​

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[Nostrum]

Just read through mis3005v3.1 document and actually you are right it doesn't mention hot water requirements having to be included in the sizing process, which is ridiculous. After all having to use an immersion heater to heat your water when your heat pump is to busy keeping up with heat loss is going to have a detrimental effect on the overall CoP when you take into account the electricity uses of the immersion!

 

[rob2048]

Hi the cylinder for ashp has a longer coil in than a standard one it needs a longer one to transfer the lower heat of the ashp worth checking one of these has been fit the immersion comes on every 15 th cycle to 60 to kill legionella hope this helps

 

[sinaloa]

Thanks Rob, It does help as I know the cylinder has a 29" element (a new cylinder was not fitted at instalation of ASHP). As the cylinder stands 60" high and I can only see immersion heater elements going to 36" it seems that to protect us against the threat of legionaires we will have to change the hot water cylinder to have a bottom mounted element or have a de-strat pump fitted.

 

[rob2048]

Hi the immersion isn't your problem I think it's your cylinder it should have been changed for one to go with ashp if not it won't get hot the coil on a suited one it longer and wider if you look on the net have a look at kingspan ones