ASHP and SunAmp cheaper than Oil tank? Confused

[Roz]

After getting a quote for burying an oil tank, and finding out that a SunAmp can replace an immersion tank (I didn't understand it when it was first mentioned to me on this forum), I'm starting to wonder if an ASHP plus SunAmp might be a lower up front cost, but I can't get my head around how to figure out whether it would be manageable going forward with monthly electricity payments. The upfront cost is more important, but that doesn't mean the monthly cost isn't important. Can anyone help me figure it out? Reason for not wanting a hot water immersion tank with the ASHP is the space limitations for 60 square metre property. 

 

Oil

Underground oil tank: £2000

Burying the tank: £1605

Oil condensing boiler: £1500

Total: £5105 plus fitting of boiler etc

 

ASHP

Air source heat pump (no tank): £1500?

SunAmp: £2000? or would I need a bigger one

Total: £3500??? plus fitting of both etc

 

Space heating fuel estimation: 6600 kwh per year

Water heating estimation: 2300 kwh per year

 

This is from our draft SAP calculations. It's just 2 adults with one bathroom at the moment. It's a 1 double and 1 single bedroom place with underfloor heating across 60 square metres (including upstairs and downstairs). I work from home so am home a lot. Double glazing. We'd also have a wood burning stove as secondary heating. 

 

Oil is about 53p per litre down here. LPG I have been given a quote for less per litre, but the restrictions about where a tank can be placed on the property make it a problem. There is no mains gas. The property is small, so I don't really want a big oil tank above ground, hence planning to bury it. 

 

Non-negotiable: 

• No above ground oil or gas storage
• Lowest upfront cost (we have a very small budget we need to stretch in every direction)
• Hot showers!

 

Also how do the energy requirements change between having an ASHP with a sunamp compared to a ASHP with an immersion tank? Can you run your DHW on just the latter? I'm feeling a bit bamboozled. I have trawled these forums so as not to bother you all but feel more confused....

 

 

 

[Cpd]

Following as this is a possible solution for me to. Thanks for asking ! 

[Ed Davies]

24 minutes ago, Roz said:

Oil is about 53p per litre down here. LPG I have been given a quote for less per litre,

 

A litre of LPG contains less energy than a litre of oil. Per kg LPG has more energy but it's quite a lot less dense which more than cancels that out. Another disadvantage of LPG is that you're tied to a single supplier (you typically rent the tank and suppliers only fill their own tanks) whereas if one supplier ups the price of their oil too much you can try somebody else.

[Russdl]

28 minutes ago, Roz said:

Underground oil tank: £2000

 

Does that include the cost of actually burying it, or just the price of the tank?

[Roz]

Just now, Ed Davies said:

 

A litre of LPG contains less energy than a litre of oil. Per kg LPG has more energy but it's quite a lot less dense which more than cancels that out. Another disadvantage of LPG is that you're tied to a single supplier (you typically rent the tank and suppliers only fill their own tanks) whereas if one supplier ups the price of their oil too much you can try somebody else.

HI Ed, Thanks. We need to discount it anyway due to the requirements about where you could place the tank, just wanted to show it had been considered  . 

[Roz]

1 minute ago, Russdl said:

 

Does that include the cost of actually burying it, or just the price of the tank?

That bits just the tank, burying it is the bit underneath, so an extra £1600 . High price for just tank as underground ones are different I believe... 

[Russdl]

12 minutes ago, Roz said:

That bits just the tank, burying it is the bit underneath, so an extra £1600

 

Bloody hell, what a clown! Sorry. Now where is my dunce's cap.

[epsilonGreedy]

I am pursuing the same low upfront cost plan as the Op and suggest it would be worth inviting an LPG supplier onsite to propose where a tank could be located.

 

I am budgeting for:

 

£250 tank supply and fit in prepared hole.

My man with his digger should excavate that in 4 hours, £100

Muck away in small skip say £130

Concrete floor in hole £ ?

£1300 Worcester 38CD combi boiler

 

All ex. VAT

 

[PeterW]

46 minutes ago, epsilonGreedy said:

£250 tank supply and fit in prepared hole.

 

Last in ground tanks we had were £2200 each, and that was for 2000 litre units.... and that was 4 years ago. 

 

Best supplier by far in that area is LPG Direct and they do underground tanks but I think they are rental only at about £20 a month. 

[Nickfromwales]

2 hours ago, Roz said:

Also how do the energy requirements change between having an ASHP with a sunamp compared to a ASHP with an immersion tank? Can you run your DHW on just the latter? I'm feeling a bit bamboozled. I have trawled these forums so as not to bother you all but feel more confused....

Oky Doky.  

At the moment, Sunamp have a PCM 34 unit which is matched to a low temp ( = or < 55oC ) ASHP. Its currently back on rapid cycle test and will re-appear in the next few months I think. In the meantime, there are other ASHP's that will do up to ( and above ? ) 65oC which will melt the PCM in a PCM 58 Sunamp unit. How the efficiency of said ASHP would be affected by this is for someone with a scientific calculator to comment on, but if you're referring to a regular ASHP and SA combo, then its a non starter at the moment.

Instead, why not use the ASHP for space heating ( as you have UFH and you're house will lend itself to be heated at flow temps as low as 35-40oC ( ? )) and enjoy having a SCoP ( seasonal average ) of maybe 2.5to 3.0, and then let the SA unit just do DHW off grid electricity? You may benefit from E10, but you'd need to work that out properly, just that if you're in in the days you'll deffo need to use heating in the colder seasons so it may as well be from E10 so cheap rate electricity into the ASHP which is a multiplier. If for eg a unit of electricity is 10p peak, then you'll be heating your home for around 4p via the ASHP.

Good that youve got UFH as it opens up some options for low grade heat.  

[Roz]

11 hours ago, Nickfromwales said:

if you're referring to a regular ASHP and SA combo, then its a non starter at the moment.

What makes it a non starter? I think I'm missing the point. In terms of what set up I'm referring to, I don't know that either. Why does ASHP charging up SunAmp not work?

 

11 hours ago, Nickfromwales said:

let the SA unit just do DHW off grid electricity?

So on E7 this would be 2300kwh per year on about 8p per kwh. £184 per year? Plus day rate of 16p per kwh for powering ASHP, £352 per year ( i divided the annual kwh space heating estimation by 3 to get this). £44 per month, plus general electricity use for appliances etc.

 

In terms of being on E7, I'd be worried about that, being at home during the day a lot.  Not on E7 I guess it would be, at 13p per kWh,  £299 for water, plus £286 for ASHP, £48.75 per month. So depends if we would spend an extra £4.75 per month on appliances (that cant be timed for night) on the E7 day rate.

 

Kerosene at 10.3 kwh per litre, makes each kwh about 5p, so to power everything on oil we'd be at £448 per year, £37 per month... 

 

Does that math seem right??

Edited December 11, 2018 by Roz
extra math for E7

[Nickfromwales]

5 minutes ago, Roz said:

What makes it a non starter? I think I'm missing the point. In terms of what set up I'm referring to, I don't know that either. Why does ASHP charging up SunAmp not work?

 

So on E7 this would be 2300kwh per year on about 8p per kwh. £184 per year? Plus day rate of 16p per kwh for powering ASHP, £352 per year ( i divided the annual kwh space heating estimation by 3 to get this). £44 per month, plus general electricity use for appliances etc.

 

In terms of being on E7, I'd be worried about that, being at home during the day a lot.  Not on E7 I guess it would be, at 13p per kWh,  £299 for water, plus £286 for ASHP, £48.75 per month. So depends if we would spend an extra £4.75 per month on appliances (that cant be timed for night) on the E7 day rate.

 

Kerosene at 10.3 kwh per litre, makes each kwh about 5p, so to power everything on oil we'd be at £448 per year, £37 per month... 

 

Does that math seem right??

E10. So you have 1pm to 4pm on off peak rate.

[Roz]

4 minutes ago, Nickfromwales said:

E10. So you have 1pm to 4pm on off peak rate.

Oh I didn't know about this! Will look it up. Sorry for missing. 

 

Can you enlighten me about the SunAmp suitability bit? I don't get it... 

[Dreadnaught]

20 minutes ago, Roz said:

Can you enlighten me about the SunAmp suitability bit? I don't get it... 

 

A SunAmp with PCM58 outputs water at 58ºC, ideal for showers, baths and space heating. But it needs an input water temperature of about 65º or so to charge it. ASHPs struggle to generate water at 65ºC*. If they do so they become much less efficient and have to work hard, which causes them wear out, and to freeze-and-defrost cycle when its cold, especially when the outside temperature is around the freezing point for reasons to do with humidity. Not good. Not recommended.

 

There is a SunAmp being developed with PCM34 (one person on here already has one). This outputs water at 34ºC and needs an input of perhaps 45ºC, which is easily generated by an ASHP. Water at 34ºC is OK for space heating but not warm enough for a shower but it can be used as a pre-heat for input to a boiler or heated tank (or indeed a SunAmp with PCM58).

 

Does that help?

 

PCM = phase-change material

ASHP = air-source heat pump

 

* there are special multi-stage ASHPs that can generate higher temperatures, but they are mechanically more complex and more expensive.

Edited December 11, 2018 by Dreadnaught

[Roz]

1 minute ago, Dreadnaught said:

 

A SunAmp with PCM58 outputs water at 58ºC, ideal for showers, baths and UFH. But it needs an input water temperature of about 65º or so to charge it. ASHP struggle to generate water at 65ºC. If they do so they become much less efficient and have to work hard, which causes them wear out, and to freeze and defrost cycle when its cold, especially when the temperature is around the freezing point for reasons to do with humidity. Not good. Not recommended.

 

There is a SunAmp being developed with PCM34 (one person on here already has one). This outputs water at 34ºC but needs an input of perhaps 45ºC, which is easily generated by a ASHP. Water at 34ºC is not warm enough for a shower but it can be used as a pre-heat for input to a boiler or heated tank.

 

Does that help?

That does help, thanks a lot. So even with a PCM34 you're looking at a set up that includes ASHP, SunAmp, plus boiler or heated tank. The heated tank we might not have space for. 

 

I'm guessing it's not going to be easy for me to figure out the energy needed to heat the water from 34 up to 60 for DHW to figure out how much that would be per month, and if it's worth the set up of an ASHP, SunAmp plus electric (?) boiler. It's a bigger initial outlay compared to ASHP and SunAmp charged from mains electric, so would need to be a good amount less per month to make it worth it for us I guess.

[Dreadnaught]

3 minutes ago, Roz said:

So even with a PCM34 you're looking at a set up that includes ASHP, SunAmp, plus boiler or heated tank. The heated tank we might not have space for. 

 

Perhaps go for simplicity. A PCM58 SunAmp charged by E10 electricity. Much less capital cost. Probably only slightly higher running costs. Fewer things to go wrong. Simpler all around. Less hassle. Small and compact too.

 

You could ask @Nickfromwales to specify the system. He knows a lot.

[Roz]

Difficult to figure it out but this kind of tariff might work well with the simple set up I guess (couldn't find much obvious information on E10). 

 

https://octopus.energy/agile/#what-does-it-cost

 

If the UFH had already come on to heat the slab pre 2pm, and SunAmp was charged at night for showers in the AM, and perhaps topped up in the AM for any baths at night... difficult to figure out how much energy everything else would use between 2pm and 7pm though at the very high peak agile rate. 

 

I think with this tariff it might be easier to switch back to a regular tariff though, as opposed to the difficulty of switching once you have an E7 or E10 metre installed (so i have read). 

 

[Roz]

28 minutes ago, Dreadnaught said:

 

Perhaps go for simplicity. A PCM58 SunAmp charged by E10 electricity. Much less capital cost. Probably only slightly higher running costs. Fewer things to go wrong. Simpler all around. Less hassle. Small and compact too.

 

You could ask @Nickfromwales to specify the system. He knows a lot.

Thanks Dreadnaught, great to get opinions. Yes @Nickfromwales any further thoughts would be gratefully received. 

[newhome]

It also depends whether you can set up the ASHP and Sunamp yourself or you need to employ someone. Neither of these are plug in and play so you may struggle to get someone who can do this at a reasonable cost. I know this from my experience of trying to get someone to fit an ASHP here. It’s much easier to find installers for traditional systems than renewables or new technology. Most installers of ASHPs are MCS certified. This means that they are used to providing quotes for RHI eligible systems that result in big money quotes. Some people on here have installed some really cheap DIY ASHPs but I’m not sure what others have paid for non MCS installs. 

[Roz]

1 minute ago, newhome said:

It also depends whether you can set up the ASHP and Sunamp yourself or you need to employ someone. Neither of these are plug in and play so you may struggle to get someone who can do this at a reasonable cost. I know this from my experience of trying to get someone to fit an ASHP here. It’s much easier to find installers for traditional systems than renewables or new technology. Most installers of ASHPs are MCS certified. This means that they are used to providing quotes for RHI eligible systems that result in big money quotes. Some people on here have installed some really cheap DIY ASHPs but I’m not sure what others have paid for non MCS installs. 

Good point NewHome. Anyone down in the south west had any decent install prices? 

[newhome]

40 minutes ago, Dreadnaught said:

You could ask @Nickfromwales to specify the system. He knows a lot.

 

Nick will help with generic questions on here I’m sure but system specification is part of his day job ?

[Dreadnaught]

On E10: https://economy10.com/overview/. I think its a bit out-of-date now but might still be useful.

[Roz]

19 minutes ago, Dreadnaught said:

On E10: https://economy10.com/overview/. I think its a bit out-of-date now but might still be useful.

Thanks Dreadnaught. I'm finding it difficult to find info directly on the suppliers websites but perhaps you have to call them to ask. 

 

Based on the Octopus Agile rate I'm now wondering if it would be better to just have ASHP plus Electric combi boiler an no sunamp. But perhaps SunAmp is more flexible if you just get it charged at night and then can use whenever rather than worrying about what time you want to take a shower.. but then less people know how to install it. 

[Dreadnaught]

17 minutes ago, Roz said:

I'm finding it difficult to find info directly on the suppliers websites but perhaps you have to call them to ask.

 

Yes I found that too. E10 (and to a lesser extent even E7) is not supported by even most electricity suppliers it seems. Some do, so if it interest you then you can find a company that will if you persevere. Having an E10 electricity meter installed can also take a bit of research too.

[Dreadnaught]

19 minutes ago, Roz said:

 Based on the Octopus Agile rate I'm now wondering if it would be better to just have ASHP plus Electric combi boiler an no sunamp. But perhaps SunAmp is more flexible if you just get it charged at night and then can use whenever rather than worrying about what time you want to take a shower.. but then less people know how to install it. 

 

Its fascinating how there really is no one-size-that-fits all. It depends so much on the individual circumstances. Its surprisingly subtle. Its why pros like @Nickfromwales take such care to look at all the parameters before recommending a complete solution.