ASHP & Sunamp - no boiler no PV

[readiescards]

Starting a new thread, as I'm struggling to understand everything in the big Sunamp thread.

 

Doing a barn conversion for a 3 double bedroom holiday cottage. 

 

Intention is to have a Panasonic 9kW ASHP feeding UFH and immersion tank (in loft space and maybe horizontal) but I'm just wondering if a Sunamp solution is better than an immersion tank - since no servicing contract, better fit in the tight space, better heat retention (no point heating the loft) - downside it will be outside my plumbers comfort zone and presumably higher capital expense. 

 

Sunamp with ASHP good idea for a holiday cottage barn conversion Yes/no?

 

FYI We are intentionally avoiding gas (LPG) since means need a boiler, extra risk (if we have gas hob), extra servicing costs, and requires tank space or a big expensive hole digging.  Ditto oil needing a tank, boiler, big hole etc.  Rhi is payable for a holiday cottage on a ASHP just requires metering but as barn won't be super insulation it will need a decent amount of heat (which perversely makes a ASHP better as it means faster Rhi payback if I understand correctly)

 

 

Thanks

Paul

 

[Nickfromwales]

First off, I don't think you can have a HP UVC in a horizontal due to the coil type / orientation. 

Next, why no pv ? You'll be paying for the hot water why not make it pay for itself ? Ground mounted array if you're not allowed 'on the roof' ?

FYI the Sunamp units will fit in a kitchen base unit. Silent and virtually maintenance free. 

 

Now, bathing. Are these going to be swanky ensuite double bedders? If so then you need bags of DHW in the morning and again in the evenings. Remember that max DHW flow rate is dictated by the cold mains flow and pressure, so pointless designing the dream hot water system if no water will come out of the taps  

[Nickfromwales]

40 minutes ago, readiescards said:

Sunamp with ASHP good idea for a holiday cottage barn conversion Yes/no?

More info needed before honestly answering that 

[readiescards]

No PV since the building is wrongly orientated and is heavily shaded by trees.

 

Bathing (outside hottub) but just one bath and one shower - so not swanky ensuite double headers.

 

Sunamp could be located in the pantry area but that is a long way from the bathroom/master bed ensuite

 

Should have decent pressure and flow since we are putting in 38mm pipe to the barn to help.

[readiescards]

Plans:

https://www.dropbox.com/s/7njj95savxlawso/LDC2025_BR01 Plans Elevs A1.pdf?dl=0

 

Note utility no longer in plan

[readiescards]

On 3/8/2018 at 22:17, Nickfromwales said:

More info needed before honestly answering that 

 

Any specific info needed? As would be great to have your thoughts before meeting the plumbers on site tomorrow morning

[Nickfromwales]

51 minutes ago, readiescards said:

 

Any specific info needed? As would be great to have your thoughts before meeting the plumbers on site tomorrow morning

Firstly, ref the G3 annual inspection. Ive yet to receive the 'bumf' from the production model 3rdGen SA units as of yet, so cannot comment on the ongoing / routine maintenance of them, but from my PoV its minimal, and maybe even just a DIY checklist / record will suffice. @AndyT ? 

3 couples aka 6 guests having 'adequate ( 10 mins @ 38oC ) showers' would need a fully charged 5kw SAPV for each couple. I know from direct experience that the SAPV when fully recharged will give 40+oC DHW flow for at least 26 minutes before dropping off to unusable heat levels, which is why Im quoting the SAPV, just fort scale.

Thats on an estimated flow of around 9/10 litres per minute. So 2 x 10 minute showers at 10LPM ( so an instantaneous delivery of 200L of bathing temp, or higher, water ) needs roughly 5kw of SA capacity. In reality it'll probably be less, but you should always allow headroom. 

So, with that capacity in mind, you'll actually need the 3rdGen Dual port SA units, and for failsafe id recommend having the units with electrical immersions in them ( so if the ASHP ever fails you can still heat hot water ). Those dual port units take non-potable ASHP water in one 'side' and discharge potable DHW via the second of the dual ports, so the same unit hydraulically separates the two bodies of water, but they're 'connected' thermally. Eg the input can be heating the cells whilst the other 'side' is discharging and if say 2kw is being drawn and 3kw is being inputted then the cells will recharge at the same time as they discharge heat.

For say a 9kw unit, the whole 9kw can be recharged by one pair of ports, and the whole 9kw can then be consumed by the second ports ( so a dual port SA isnt looked upon to be 4.5kw to one and 4.5kw to the other if that makes sense? ). Another benefit of this is the connections are 22mm, so an electrically heated SA DP can be used solely for DHW with cold mains going into one side of each port ( 2 x 22mm inlets ) and then be paralleled through the SA to give a combined ouput of the equivalent of a 44mm pipe flow rate. Therefore its safe to say these can be configured to deliver masses of instant DHW with flow rates of 30 - 40 litres per min achieved with ease ( so 3 good showers running simultaneously with ease plus a bit of room to draw off for a kitchen sink tap / other at the same time too ). That would obviously be dependant on the cold mains being sufficient to deliver such high flow rates, but easily achieved with a correctly sized cold mains accumulator. 

All this can also easily be achieved by a large HP UVC just then you have the annual servicing and inspections, which is a reasonably high outgoing over the life of the UVC ( as a good stainless steel UVC should outlive you ). The 9kw sunamp units are about the size of a slimline dishwasher so will fit under a kitchen / utility worktop too. An equivalent UVC would stand about 1600 - 1800mm heigh, and be about 600mm wide. 

 

[ProDave]

On 09/03/2018 at 08:34, readiescards said:

No PV since the building is wrongly orientated and is heavily shaded by trees.

 

So is ours which is why the pv will be ground mounted out of the way of the trees

 

[readiescards]

Does an ASHP require a buffer tank if used with Sunamps?  What would be the pros and cons?  ta

[Nickfromwales]

No need for the buffer with the SA as the flow rate through the heat exchanger is more than sufficient to not cause issues for the pump ( eg it's flowing through an open circuit ) as it's not driving the pump into a blending valve like it would if it were an UFH manifold. The issue arises when you could be pumping to a partially or fully closed valve, but apart from a zone valve that issue doesn't exist with this ( ASHP > SA ) configuration. 

The beauty is that these really can be 'single box' solutions. I'm eagerly awaiting my training on these which I'm hoping will be soon after the 3rd gen stuff is to market. 

[readiescards]

ASHP -> (SA & UFH)

 

If the SA is fully charged and the UFH only needs a trickle of heat so a blending valve might be partially open only - is that an issue with no buffer tank?

 

Reason for asking my local plumber tells me the ASHP would need a buffer tank  (and I'm assuming a buffer tank needs the yearly servicing that I'm trying to avoid - does it?)

[Nickfromwales]

2 hours ago, readiescards said:

ASHP -> (SA & UFH)

 

If the SA is fully charged and the UFH only needs a trickle of heat so a blending valve might be partially open only - is that an issue with no buffer tank?

 

Reason for asking my local plumber tells me the ASHP would need a buffer tank  (and I'm assuming a buffer tank needs the yearly servicing that I'm trying to avoid - does it?)

Ah sorry. Just adjusted my thinking from the current couple of installs I'm speccing ( as their SA units are being used half and half, heating / hot water ). 

A low loss header will suffice here I think. No stored pressurised hot water volume exceeding 15litres in any one device and no need for annual inspections. 

ASHP > SA via a 2-port zone valve. 

ASHP > LLH via a 2-port zone valve. 

LLH > UFH / space heating. 

You can simply accept some short cycling, not much, with the LLH accepting it's a cheaper and easier solution, or fit another SA unit as half buffer / half DHW uplift. Then you can reduce the size of the DHW SA units.

They're an elegant solution, and save annual inspections, so in 10 years you'll be paid up on the heating buffer unit, will have saved energy producing DHW, won't need any complex plumbing or controls, and won't have any major standing losses, so it's down to paying a bit more up front, with a view to some payback from the reduced associated ongoing costs. 

 

[Nickfromwales]

Oh, and as your pushing on with this project, consider the lead times with the sunamp . May be game over if they can't get them to you quickly enough. 

[readiescards]

What is the lead time?

[Nickfromwales]

You need to ask SA. Maybe @AndyT can advise. Ping him a PM. 

[Nickfromwales]

Oh, and you need to work out what your going to fit first of course  

[andy]

On 17/03/2018 at 08:21, Nickfromwales said:

Ah sorry. Just adjusted my thinking from the current couple of installs I'm speccing ( as their SA units are being used half and half, heating / hot water ). 

A low loss header will suffice here I think. No stored pressurised hot water volume exceeding 15litres in any one device and no need for annual inspections. 

ASHP > SA via a 2-port zone valve. 

ASHP > LLH via a 2-port zone valve. 

LLH > UFH / space heating. 

You can simply accept some short cycling, not much, with the LLH accepting it's a cheaper and easier solution, or fit another SA unit as half buffer / half DHW uplift. Then you can reduce the size of the DHW SA units.

They're an elegant solution, and save annual inspections, so in 10 years you'll be paid up on the heating buffer unit, will have saved energy producing DHW, won't need any complex plumbing or controls, and won't have any major standing losses, so it's down to paying a bit more up front, with a view to some payback from the reduced associated ongoing costs. 

 

Hi all

 

New poster on the forum and need to decide what on earth I can do for DHW/UFH.  It seems like the above would be a good fit for my solution too but I'm not too clear what the half buffer idea is?

 

My plans at present are to install:

 

• 6kW PV (about - up to max for a single phase is the aim here)
• Wet UFH
• ASHP (I am on mains gas but morally I don't want to use it plus don't want to pay the re-connection cost as it's now capped at the road)
• Tesla Powerwall 2 - although appreciate the conflict of this for storage vs. Sunamp
• Sunamp(s) for DHW/buffer for UFH?

My annual heat load is anticipated to be circa 4,000kWh/a and DHW probably about 2,000kWh/a.  House will be near passive but not quite there due to shape.

 

I really like the concept of Sunamp but I'm getting a bit lost on the new UniQ model range and what the best design is for my requirements.

 

Hopefully the above all makes sense and happy to provide more info if that helps.

 

Cheers

Andy

[Jeremy Harris]

Welcome @andy,

 

With that sort of annual energy use then it's worth looking at the costs carefully.  6,000 kWh p.a. will cost somewhere around £1,000 p.a, assuming a standard single tariff, rather than an off-peak one, and assuming no PV self-consumption.

 

The battery will never ever pay for itself, or come close, even with direct electric heating.  With a heat pump to reduce the demand, plus a Sunamp to reduce the DHW demand, then no battery will come close to covering its cost, and especially not the very expensive Tesla Powerwall - it will die from old age long before the cost has been recovered.

 

Your heating demand and DHW demand seem to be back to front to me.  It's more normal in a  well-insulated house for the DHW demand to be higher, or no more than equal to, the heating  energy usage.  In our case just nearly 2/3rds of our energy goes to heating hot water, for example.  However, assuming your 2000 kWh for hot water is accurate, then that equates to around 6 kWh per day, allowing for holidays.  A single Sunamp UniQ 9 kWh model can meet that requirement with energy to spare, and can be charged by a mix of excess PV for around 8 months of the year and direct electricity for the remaining time.  It's debatable whether it's worth using an off-peak tariff for winter use, as the standing charge and day time unit price may well make that a more expensive option, but as tariffs vary widely across the country it's worth doing your own comparison.

 

The 4000 kWh heating demand seems high to me.  Our heating energy requirement is typically around 1500 kWh for a 130 m² house.  We use a small ASHP, but it's marginal as to whether that is cost effective, balancing capital investment versus energy cost saving through life.  The total cost of our ASHP install came to under well £2000 (with a DIY installation), and that much money would buy well over 15 years of additional electricity, so unless the ASHP lasts in excess of 15 years it won't ever pay for itself.

 

In terms of environmental impact, then it's very questionable as to whether buying expensive bits of kit, that have a significant manufacturing environmental impact, makes sense.  If I had mains gas available I'd use it, without question, as it would be far cheaper to run and offer an overall lower environmental impact through life than a solution using a heat pump.  You can still combine heat energy storage, using something like a Sunamp, with a high efficiency condensing combi boiler, and so save a great deal of your DHW energy cost, and reducing your overall environmental impact a great deal.  However, the biggest difference you can make, in environmental impact terms, is reduce the very high 4000 kWh heating demand.

 

Our house is all-electric, not from choice, but because we don't have a gas supply anywhere nearby.  We still managed to get an environmental impact rating that equates to -0.9tonnes of CO₂ per year.  The latter is roughly equivalent to having our plot covered with 42 mature broadleaved trees, in terms of CO₂ sequestration.  With an efficient gas combi, plus your 6 kWp of PV and a Sunamp, you could easily get a much better environmental impact rating than this, as we're penalised for using electricity, which is "dirtier" than mains gas by a significant amount.

[Ed Davies]

11 minutes ago, JSHarris said:

as we're penalised for using electricity, which is "dirtier" than mains gas by a significant amount.

 

Maybe it is in SAP but in the real world, I'm not so sure as back-of-envelope calculations with actual grid intensities show they're much more evenly balanced. I've read that the SAP numbers (gCO₂e/kWh) are being revised down to more closely match actual grid numbers over the last few years. Of course, there are complications:

 

1) Space heating (as opposed to DHW) needs to be evaluated against the grid carbon intensity over the heating season, not the whole year.

 

2) In the short term any increase in electricity demand will likely be met mostly by gas-fired generation so the marginal intensity will be higher than the average intensity but

 

3) in the longer term new generation capacity will likely mostly come from renewables and, perhaps, other low-carbon generation (i.e, nuclear) so in that sense adding new electricity demand should eventually reduce the average intensity.

 

Financially gas is probably cheaper but if your demand is low the standing charge can't be ignored completely.

[andy]

41 minutes ago, JSHarris said:

Welcome @andy,

 

With that sort of annual energy use then it's worth looking at the costs carefully.  6,000 kWh p.a. will cost somewhere around £1,000 p.a, assuming a standard single tariff, rather than an off-peak one, and assuming no PV self-consumption.

 

The battery will never ever pay for itself, or come close, even with direct electric heating.  With a heat pump to reduce the demand, plus a Sunamp to reduce the DHW demand, then no battery will come close to covering its cost, and especially not the very expensive Tesla Powerwall - it will die from old age long before the cost has been recovered.

 

Your heating demand and DHW demand seem to be back to front to me.  It's more normal in a  well-insulated house for the DHW demand to be higher, or no more than equal to, the heating  energy usage.  In our case just nearly 2/3rds of our energy goes to heating hot water, for example.  However, assuming your 2000 kWh for hot water is accurate, then that equates to around 6 kWh per day, allowing for holidays.  A single Sunamp UniQ 9 kWh model can meet that requirement with energy to spare, and can be charged by a mix of excess PV for around 8 months of the year and direct electricity for the remaining time.  It's debatable whether it's worth using an off-peak tariff for winter use, as the standing charge and day time unit price may well make that a more expensive option, but as tariffs vary widely across the country it's worth doing your own comparison.

 

The 4000 kWh heating demand seems high to me.  Our heating energy requirement is typically around 1500 kWh for a 130 m² house.  We use a small ASHP, but it's marginal as to whether that is cost effective, balancing capital investment versus energy cost saving through life.  The total cost of our ASHP install came to under well £2000 (with a DIY installation), and that much money would buy well over 15 years of additional electricity, so unless the ASHP lasts in excess of 15 years it won't ever pay for itself.

 

In terms of environmental impact, then it's very questionable as to whether buying expensive bits of kit, that have a significant manufacturing environmental impact, makes sense.  If I had mains gas available I'd use it, without question, as it would be far cheaper to run and offer an overall lower environmental impact through life than a solution using a heat pump.  You can still combine heat energy storage, using something like a Sunamp, with a high efficiency condensing combi boiler, and so save a great deal of your DHW energy cost, and reducing your overall environmental impact a great deal.  However, the biggest difference you can make, in environmental impact terms, is reduce the very high 4000 kWh heating demand.

 

Our house is all-electric, not from choice, but because we don't have a gas supply anywhere nearby.  We still managed to get an environmental impact rating that equates to -0.9tonnes of CO₂ per year.  The latter is roughly equivalent to having our plot covered with 42 mature broadleaved trees, in terms of CO₂ sequestration.  With an efficient gas combi, plus your 6 kWp of PV and a Sunamp, you could easily get a much better environmental impact rating than this, as we're penalised for using electricity, which is "dirtier" than mains gas by a significant amount.

 

Thanks for the welcome and detailed reply @JSHarris.

 

The 4,000kWh/a has come from our PHPP consultant but it seems high to me too!  I have just asked him to check this as I think we should be coming in at circa 17.5kWh/m2a on a 142m2 house, which brings us down to about 2,500kWh/a heating demand.

 

Our DHW demand is low as there's only 2 of us and we only shower on the weekends (gym before work during week before anyone says anything!) but we need to ensure it's sized correctly to be able to deliver DHW for a 3/4 bed/2 bathroom house when occupied fully.

 

I hope that our excess PV will be doing 2 jobs:

 

1. Run the day to day requirements of the house

3. Top up Sunamp until it's full

3. Once the Sunamp is full, top up the Powerwall

 

Planning to have an E7/E10 tariff and during off-peak the Powerwall and/or Sunamp will top up if required (e.g. in the winter) but I haven't done the calculations on this.

 

When we're not covered by PV, the house uses Powerwall first and only if that is empty do we resort to mains feed.

 

For me, saying not gas and yes to Powerwall isn't so much about the money but about trying to not consume from the grid as much as possible, which Powerwall will help us achieve.  I don't mind being a (relatively) early adopter of this and paying a premium.

 

The Sunamp UniQ 9 model - how does the "half buffer" concept fit into this?  I am guessing it's something like UFH and DHW go into an initial Sunamp which outputs at a temperature suited to UFH and the the DHW goes into a second Sunamp for heating to e.g. 55C?

[ProDave]

It is all very good to care about the environment, you are doing that by building a low energy house, fitting PV, and an efficient means to store hot water (the Sun amp)

 

However I am not convinced about the battery storage.  I suspect you won't have that much surplus PV to charge it with.  I keep looking at battery storage, but we are "not there yet" Even if all the electricity to charge is free, it still looks unlikely you will have paid back the capital cost by the time the batteries need replacing. What is the environmental cost of those end of life batteries to dispose of?

 

The idea of charging them with off peak electricity is equally dubious.  To get an off peak tariff you pay a much higher daytime rate and a higher standing charge. It is not just viable for this imho.

 

I want battery storage for my own house eventually. I am still thinking that will eventually be a DIY built system with NiFe batteries. At least I know with those there is a reasonable chance of the batteries lasting until I fall off my perch so it should be a buy once system.

 

One of the best things you can do to self use as much PV as possible is use the big appliances like Dishwasher, washing machine and tumble dryer one at a time close to the middle of the day. If you are out at work you would need to do that with timers.

[Jeremy Harris]

43 minutes ago, Ed Davies said:

 

Maybe it is in SAP but in the real world, I'm not so sure as back-of-envelope calculations with actual grid intensities show they're much more evenly balanced. I've read that the SAP numbers (gCO₂e/kWh) are being revised down to more closely match actual grid numbers over the last few years. Of course, there are complications:

 

1) Space heating (as opposed to DHW) needs to be evaluated against the grid carbon intensity over the heating season, not the whole year.

 

2) In the short term any increase in electricity demand will likely be met mostly by gas-fired generation so the marginal intensity will be higher than the average intensity but

 

3) in the longer term new generation capacity will likely mostly come from renewables and, perhaps, other low-carbon generation (i.e, nuclear) so in that sense adding new electricity demand should eventually reduce the average intensity.

 

Financially gas is probably cheaper but if your demand is low the standing charge can't be ignored completely.

 

 

Yes, it's a slight distortion in the version of SAP that we were assessed under, and the grid is certainly getting cleaner, with the increase in renewable capacity, and decrease in coal, but the the grid still emits around 58 million tonnes of CO₂ (2018 predicted outcome, 2017 was 60 million tonnes CO₂), which with the generated annual energy fairly stable at around 336 TWh.  The 2017 CO₂ grid intensity data (all fuels, including nuclear and renewables) was 225 tonnes of CO₂ per GWh of generation, so about 0.225 kg CO₂/kWh, but that excludes all the distribution losses (typically around 10 to 15%, I believe), so the reality at the point of consumption is a CO₂ intensity figure of closer to 0.25 kg CO₂/kWh.  Assuming a condensing gas boiler with an efficiency of 85% (on the low side of what's reasonable, IMHO) then burning gas this way generates around 0.211 kg CO₂/kWh.  A 90% efficient condensing boiler decreases this to about 0.2 kg CO₂/kWh.

 

My guess is that the electricity grid might reach parity with an efficient gas boiler in around 10 to 15 years time, looking at the current trends, but that's about the lifetime for either a gas boiler or an ASHP, so the better environmental solution for the nest few years would be an efficient gas boiler, looking to change to a heat pump, CHP or other less CO₂ intensive solution in 10 to 15 years time.

 

 

 

 

[Jeremy Harris]

I keep a running spreadsheet of battery system performance and pricing, and none yet look worthwhile in terms of any benefit to the environment, nor do any come close to covering the capital outlay through life.  The closest to look as if it may, possibly, make sense in a few years time is the Sofar system (around £3,000 including VAT for a 7.2 kWh system), as the capital cost is lower, plus it offers some performance advantages, including a limited ability to run off-grid during a power cut.  For us the latter is an attraction that might swing us towards buying one in a year or two, although we know that we'll still never recover the investment, and we have 6.25 kWp of PV, facing more or less South, on a 45 deg pitch that slightly improves winter performance.

 

PV generation for us still falls off a cliff in October each year, and we don't start to generate anything meaningful again until the beginning of March, and that has a big impact on the usefulness of energy storage, either as heat in the Sunamp Uniq eHW 9 that we have, or in any battery system.  To all intents and purposes you can forget about being able to get any excess PV generation for around 3 to 4 months of the year, the very time when the heating demand and other household energy demands, like lighting, will be greatest.

 

 

[andy]

27 minutes ago, ProDave said:

What is the environmental cost of those end of life batteries to dispose of?

 

On that front, the batteries are fully recyclable:

 

https://www.tesla.com/en_GB/blog/teslas-closed-loop-battery-recycling-program

[andy]

32 minutes ago, ProDave said:

The idea of charging them with off peak electricity is equally dubious.  To get an off peak tariff you pay a much higher daytime rate and a higher standing charge. It is not just viable for this imho.

 

I want battery storage for my own house eventually. I am still thinking that will eventually be a DIY built system with NiFe batteries. At least I know with those there is a reasonable chance of the batteries lasting until I fall off my perch so it should be a buy once system.

 

One of the best things you can do to self use as much PV as possible is use the big appliances like Dishwasher, washing machine and tumble dryer one at a time close to the middle of the day. If you are out at work you would need to do that with timers.

 

I will need to do the calculations to see if the off-peak is worthwhile as like you say it may not be.  This area could change with demand based pricing which the Powerwall will hopefully be aware of, so it would fill up at the cheapest time possible and then everything else draws off that.

 

Another benefit of the Powerwall is you aren't tied to using the PV energy when the sun is actually shining, so you're able to shift that utilisation to fit your realistic usage patterns but it still makes sense to use such appliances when there's an excess of energy available.