Alternatives To An ASHP

[SteamyTea]

19 minutes ago, Matt60 said:

I wonder how that would stack up cost wise to run each year.

Start with Excel, your existing bills and PVGIS

https://re.jrc.ec.europa.eu/pvg_tools/en/#PVP

[Matt60]

15 minutes ago, SteamyTea said:

Start with Excel, your existing bills and PVGIS

https://re.jrc.ec.europa.eu/pvg_tools/en/#PVP

 

Thanks for your reply, that comes out at approx 4kwh on that link from PV. My current (last house - now renting while building) was on oil and so the bills on that won't help me much as both heating and hot water was via the oil. What I'd like to know is how much it would cost to heat and do the hot water via emersion and electric boiler in the new house. If I had an idea what that would be I just need to subtract the afore mentioned PV contribution and then I can assess it against other systems.

[Thedreamer]

A well done self build requires little to no heating. I didn't see the point investing in an expensive heating system that would be rarely used.

 

Have you considered an exhaust heat pump? Our one acts as MEV, but you can connect it to extract air from the outside like a conventional heat pump if you already have MVHR in your design.

 

 

 

 

[Iceverge]

I did hours and hours of sums and spreadsheets on this one. 

 

The best year round solution I could come up with was build a passive house. (square and simple with no conventional heating system worked out cheaper than a building regs house). Note mains gas isn’t an option for us.

 

Provide space heating using an air to air heat pump. 

Heat DHW via night rate electricity. 

Install 4kw pv to help DHW in summer.

 

It was a pretty close run thing with omitting the PV and using an ASHP for space heating and DHW but the initial capital cost was conservatively €4000 higher. The break even point was 20 years when the ASHP became cheaper (using an optimistic COP of 3 for DHW and heating). Even after 25 years the ASHP was only in the lead by €800. That was assuming it ran flawlessly for all that time and I ignored the extra cost of interest on the €4k. Note the sums would sway drastically towards the ASHP if we had a conventional heat demand.

 

We went with the former as a plan. At the moment we have a 2kw resistive heater in the hall(€35) providing space heating (€2.56/day for 20deg everywhere) and a 300l direct UVC providing hot water ( Using about €1 per day for 2 showers and a bath). We haven’t installed the a2a unit yet or the PV. 

 

I’m going to monitor the first year and see how we get on in actual usage before redoing my sums. I have a sneaking suspicion that we’ll never install anymore heating but we probably will put in PV. 

 

[SteamyTea]

9 hours ago, Matt60 said:

What I'd like to know is how much it would cost to heat and do the hot water via emersion and electric boiler

Physics

 

Specific Heat Capacity of Water = 4.18 kJ.kg^-1.K-¹

 

So say you want to heat 200 litres of water from 8°C to 50°C

 

4.18 [ kJ.kg^-1.K-¹] X 200 [kg] X (50 - 8) [°C] = 35115 kJ

 

To convert kJ to kWh, multiply by 0.0002777

 

35115 [kJ] X 0.0002777 = 9.75 kWh

 

Assuming a 2.8 kW immersion heater, to calculate the time taken to heat

 

9.75 [kWh] / 2.8 [kW] = 3.48 hours

 

Assuming two prices for electricity, E7 at 10p. kWh^-1 and Standard at 16p.kWh^-1

 

9.75 [kWh] x 0.1 [£.kWh^-1] = 0.975 [£]

 

9.75 [kWh] x 0.16 [£.kWh^-1] = 1.56 [£]

 

 

Edited March 2, 2021 by SteamyTea

[Bramco]

2 hours ago, SteamyTea said:

9.75 [kWh] x 0.1 [£.kWh^-1] = 0.975 [£]

 

9.75 [kWh] x 0.16 [£.kWh^-1] = 1.56 [£]

 

And you won't need to heat the whole tank from 8 to 50 every day, in fact if you have PV then it may only be half the year and the other half only half the tank on average.

 

So £1 on E7 for maybe a quarter of the time - ~£90. Even if it is £200, there's a lot of £200s in the cost of an ASHP.  Obviously if you wanted to also cover UFH with a similar solution then you'd need to add in an estimate for that as well.

 

Now you've got me thinking - do I really need that ASHP or can I manage with a simple UVC with immersion heaters and Willis heaters for the UFH as mentioned on some other threads.

 

Simon

[SteamyTea]

7 minutes ago, Bramco said:

Now you've got me thinking - do I really need that ASHP or can I manage with a simple UVC with immersion heaters and Willis heaters for the UFH as mentioned on some other threads.

This is the problem I have.

With small power loads, it is not worth me fitting an ASHP.

 

[epsilonGreedy]

12 minutes ago, Bramco said:

Now you've got me thinking - do I really need that ASHP or can I manage with a simple UVC with immersion heaters and Willis heaters for the UFH as mentioned on some other threads.

 

 

This is my interim plan.

 

One of the BuildHub forum myths is that ASPHs are no more expensive to install than a gas boiler. This is based on a few forum leading lights who sourced their barebones ASPH units off eBay and installed themselves. The ordinary self builder who has not created a passiv house will have to overspec the ASHP to avoid frosting problems and the all too typical woes of an undersized ASHP which gets us to a starting price of £7k. Then those not up to speed in DIY ashp installs will encounter premium labour rates for installing exotic eco technology.

[Iceverge]

39 minutes ago, SteamyTea said:

This is the problem I have.

With small power loads, it is not worth me fitting an ASHP.

 

 

Hardly a problem. More lightly the solution I'd say. 

[SteamyTea]

22 minutes ago, Iceverge said:

More lightly the solution I'd say. 

It is those few times a year when my space heating load doubled.

Not much in the scheme of things, but hurts at the time.

Heating is off now.

Edited March 2, 2021 by SteamyTea

[Matt60]

11 hours ago, Bramco said:

 

do I really need that ASHP or can I manage with a simple UVC with immersion heaters and Willis heaters for the UFH as mentioned on some other threads.

 

Simon

 

Pretty much exactly what I'm think except supplemented by PV and a battery bank to take the edge off the yearly cost. That said, the PV and battery could always be retro fitted once running costs are established. I intend to have a bottle fed gas fire with back-boiler (can clain the VAT back as it would be part of the hot water system) which will heat much of the hot water in the winter.  I also wonder if instead of an immersion heater and willis' if a electric boiler would be better to do both?

Edited March 2, 2021 by Matt60

[NSS]

57 minutes ago, Matt60 said:

 

Pretty much exactly what I'm think except supplemented by PV and a battery bank to take the edge off the yearly cost. That said, the PV and battery could always be retro fitted once running costs are established. I intend to have a bottle fed gas fire with back-boiler (can clain the VAT back as it would be part of the hot water system) which will heat much of the hot water in the winter.  I also wonder if instead of an immersion heater and willis' if a electric boiler would be better to do both?

Indecisions, indecisions, indecisions.

[joe90]

9 hours ago, Matt60 said:

 I also wonder if instead of an immersion heater and willis' if a electric boiler would be better to do both?

They will  give the same cost to run but cost of immersion and Willis is as cheap as chips, no idea of electric boiler costs to instal. Once the infrastructure is in you can always change the heat source at a later date .

[jack]

12 hours ago, Matt60 said:

Pretty much exactly what I'm think except supplemented by PV and a battery bank to take the edge off the yearly cost. That said, the PV and battery could always be retro fitted once running costs are established. I intend to have a bottle fed gas fire with back-boiler (can clain the VAT back as it would be part of the hot water system) which will heat much of the hot water in the winter.  I also wonder if instead of an immersion heater and willis' if a electric boiler would be better to do both?

 

Have you looked into the cost of batteries and the associated hardware, and done the sums based on how much energy you can realistically buffer? I'd be really surprised if there's a net financial benefit to a battery system in a low-energy house over, say, a 10 year period.

 

Even with PV, the problem remains: over winter, you don't generate much energy, so your batteries will be underused. Over summer, there's often so much insolation that you don't have a hope of using it all, so your batteries will be full early in the day and you still end up exporting. Shoulder months can be better, but even then it's hard to model day-to-day activities unless you have a good handle on how energy is used (or will be used) in the new house.

 

I don't know whether these very cheap overnight tariffs from, eg, Octopus change the numbers much, but I personally think there are a lot of numbers to be crunched before making decisions like these.

[newhome]

2 hours ago, jack said:

I don't know whether these very cheap overnight tariffs from, eg, Octopus change the numbers much, but I personally think there are a lot of numbers to be crunched before making decisions like these.

They do change the numbers a lot. Last summer the overnight rates were peanuts, and even negative on occasion but they have been relatively high over the last month or so apparently. You really need to work out costs for a year to get a proper view of how much money you can save. 

[jack]

7 minutes ago, newhome said:

They do change the numbers a lot. Last summer the overnight rates were peanuts, and even negative on occasion but they have been relatively high over the last month or so apparently. You really need to work out costs for a year to get a proper view of how much money you can save. 

 

Makes it even more difficult then.

[SteamyTea]

12 minutes ago, newhome said:

They do change the numbers a lot. Last summer the overnight rates were peanuts, and even negative on occasion but they have been relatively high over the last month

Comes as no surprise that the price goes up with demand, it would be really odd i it went the other way.

 

Prices tend  get closer to the mean price, that is the idea of offering variable pricing.

It is not being offered to be nice for the end consumer, it is all about the generation side becoming more efficient.

 

[newhome]

26 minutes ago, SteamyTea said:

Comes as no surprise that the price goes up with demand, it would be really odd i it went the other way.

 

Prices tend  get closer to the mean price, that is the idea of offering variable pricing.

It is not being offered to be nice for the end consumer, it is all about the generation side becoming more efficient.

 

Yes indeed and I wouldn’t expect the figures to be constant throughout the year. But you do have to do some fairly detailed sums to see if the numbers stack up. I’m pretty sure that a flexible tariff would work for me once I’m able to move to one. 
 

 

[pdf27]

8 hours ago, jack said:

Have you looked into the cost of batteries and the associated hardware, and done the sums based on how much energy you can realistically buffer? I'd be really surprised if there's a net financial benefit to a battery system in a low-energy house over, say, a 10 year period.

 

Even with PV, the problem remains: over winter, you don't generate much energy, so your batteries will be underused. Over summer, there's often so much insolation that you don't have a hope of using it all, so your batteries will be full early in the day and you still end up exporting. Shoulder months can be better, but even then it's hard to model day-to-day activities unless you have a good handle on how energy is used (or will be used) in the new house.

 

I don't know whether these very cheap overnight tariffs from, eg, Octopus change the numbers much, but I personally think there are a lot of numbers to be crunched before making decisions like these.

 

Interesting modelling study done here which nicely shows this - Passivhaus with a big PV array generating 11 MWh/year and consuming 4 MWh/year.

• With no battery they were predicting 2.2 MWh/year would come from PV.
• With a 5 kWh battery they were predicting 2.9 MWh/year would come from PV (700 kWh/year saving, worth about £70).
• With a 10 kWh battery they were predicting 3.1 MWh/year would come from PV (900 kWh/year saving, worth about £90).
• With a 40 kWh battery they were predicting 3.3 MWh/year would come from PV (1100 kWh/year saving, worth about £110).

It's worth noting that they could probably have saved ~200 kWh/year by switching the dishwasher from cold fill to hot fill and another 150kWh/year by doing the same with the washing machine, as well as increasing the fraction PV directly used by both as hot water can be time shifted more easily.

 

If you want to have a battery - say you have issues with the reliability of your electricity supply - then it really doesn't matter how much it is, you get nearly all the savings from a very small battery. The PV in that case (well, if it were possible to export it all - they had a severe export limit) would be worth ~£770, and at current prices the system would not have cost much more than a 13 kWh battery.

[jack]

18 minutes ago, pdf27 said:

It's worth noting that they could probably have saved ~200 kWh/year by switching the dishwasher from cold fill to hot fill and another 150kWh/year by doing the same with the washing machine, as well as increasing the fraction PV directly used by both as hot water can be time shifted more easily.

 

I looked into this when we were doing our house. Many (most?) dishwashers and washing machines no longer have a hot fill capability, in the sense of having separate hot and cold inlets. From memory, some machines have a relatively low maximum water temperature at their single inlet.

 

You can't cold rinse with a single inlet machine if it's connected to hot water.

 

Also, the relatively low water consumption of modern machines would have meant the need for a hot water loop for each of these devices, because otherwise you'd be filling with cold water until it heated up. Since we weren't planning a hot loop, it all seemed like a lot of extra effort and cost.

[SteamyTea]

1 hour ago, pdf27 said:

Interesting modelling study done

I did a modelling study a few years back and found that it was better, for grid stability and reducing the large local losses, to just fit houses with small, <1 kWh, 3 kW power, batteries and inverters.

 

I think the major problem with a PV/battery storage system is that the UK has clearly defined seasons due to our latitude.

PV with battery storage may work well below the 'sunshine belt' sub 40° latitude (draw a line around the world that passes though Toronto and Madrid and that is the line that gives peak, land based, solar production), just not really viable in the UK.

Even that large Tesla battery storage in Victoria, Australia, is for short term grid stability, not long term energy storage.

 

If you really want to store PV energy, stick it in a water cylinder.  Any left over can go into the grid and help lower all our emissions.  All the incentives are about lowering emissions, not individuals personally benefitting financially.

If you want to financially benefit from lower emissions, use less energy in everything you do.  For the last half hour my house has been drawing 30W.  The heating has been off since Sunday.  It is 20.7° where I am sitting.  And my car is doing 53 MPG, which is 1.2 kWh/mile, or about 3 times what a BEV uses, but still pretty good for 1.6 tonnes of steel.

This gives me a dilemma.  Fitting a new ASHP system will cost about the same as buying a second hand BEV.  My house uses around 5 MWh/year, my car about 30 MWh/year.

I will be financially better off getting a newer car, and the environment will benefit as well.

And I may get my first car with a warning when the windshield washer bottle is getting low, and an mp3 player.

Edited March 3, 2021 by SteamyTea

[ProDave]

My conclusion is up to a typical 4kW PV system, it is very easy to self use all that you generate.  So a lot of what we generate goes into the washing machine, dishwasher, or tumble dryer, not into "heating" the house.  So what.  as long as it is used somehow, it reduces what we have to import and pay for.  What can't be used goes to DHW and then only a tiny bit gets exported.

 

It is only above 4kW of PV that it becomes hard to self use it all and battery storage might make more sense.

 

@SteamyTea post highlights the difference between the extreme ends of the UK.  After our brief warm spell, it's been back down to 3 degrees sitting under a cold grey dark sky (Harr) up here, so there is no way we can turn the heating off yet (though last week it was not doing much work).  Our heating bills with the new house up here are pretty low.  I bet they would be stupidly low if this house was in the warmer climate where @SteamyTea lives.

[pdf27]

1 hour ago, jack said:

 

I looked into this when we were doing our house. Many (most?) dishwashers and washing machines no longer have a hot fill capability, in the sense of having separate hot and cold inlets. From memory, some machines have a relatively low maximum water temperature at their single inlet.

 

You can't cold rinse with a single inlet machine if it's connected to hot water.

 

Also, the relatively low water consumption of modern machines would have meant the need for a hot water loop for each of these devices, because otherwise you'd be filling with cold water until it heated up. Since we weren't planning a hot loop, it all seemed like a lot of extra effort and cost.

For dishwashers it's pretty simple - they've only got a single inlet, but most (not all) will take water at up to 60°C. I switched from cold to hot fill at a previous house where we had a pretty rubbish Smeg dishwasher picked up off Gumtree and it was a revelation - cleaning was vastly better and it ran through cycles much faster. Typically they use about 10 litres per wash for the more efficient ones - about a bucket of water - and if your plumbing takes anything like that before it runs warm you've got a problem. Any cold slug isn't a big deal - essentially they fill up with the required amount of water, and then the electrical heater kicks in to warm it to the temperature required by the cycle (which is why hot fill runs faster). I just teed it off the kitchen sink and didn't worry about it after that.

Hot fill washing machines is rather more controversial - it only works if you supply both hot and cold fill to the machine, and there is only one manufacturer I'm aware of who does them (Ebac). I'm not convinced that they're particularly valuable, especially as washes are getting colder over time, but £100 extra for 150 kWh/year is a better deal than £7k extra for 1000 kWh/year: not that either is good or you could keep a straight face describing them as an investment, but the washing machine is significantly less bad.

 

10 minutes ago, SteamyTea said:

I did a modelling study a few years back and found that it was better, for grid stability and reducing the large local losses, to just fit houses with small, <1 kWh, 3 kW power, batteries and inverters.

 

I think the major problem with a PV/battery storage system is that the UK has clearly defined seasons due to our latitude.

PV with battery storage may work well below the 'sunshine belt' sub 40° latitude (draw a line around the world that passes though Toronto and Madrid and that is the line that gives peak, land based, solar production), just not really viable in the UK.

Even that large Tesla battery storage in Victoria, Australia, is for short term grid stability, not long term energy storage.

 

If you really want to store PV energy, stick it in a water cylinder.  Any left over can go into the grid and help lower all our emissions.  All the incentives are about lowering emissions, not individuals personally benefitting financially.

There's an additional problem - the battery controllers out there are the moment are pretty dumb, and don't really connect to what the grid actually wants. If you've got PV at home batteries will try to charge off it rather than export, even if there is a lot of demand during the day with the gas plants working hard but they're expecting a storm with loads of wind to hit that night and drive spot rates negative.

Hot water storage makes sense with a very large cylinder, and I'd also argue for a very well insulated house a thermostat which turns up and down in response to electricity prices makes sense too. Well insulated houses - particularly ones with cellulose insulation - seem to have a time constant in the region of 24 hours, and that effectively allows you to use the house itself for a lot of thermal storage.

 

10 minutes ago, ProDave said:

My conclusion is up to a typical 4kW PV system, it is very easy to self use all that you generate.  So a lot of what we generate goes into the washing machine, dishwasher, or tumble dryer, not into "heating" the house.  So what.  as long as it is used somehow, it reduces what we have to import and pay for.  What can't be used goes to DHW and then only a tiny bit gets exported.

 

It is only above 4kW of PV that it becomes hard to self use it all and battery storage might make more sense.

The problem is that for a bigger system you're going to be MCS registered so can be paid for what you export. That means you're only saving the difference between the export rate (5p or so) and the ~15p you're paying, for the 20% or so of your total consumption that your battery can provide - overnight loads in summer, basically. It really doesn't add up to much money.

 

The only way I can almost make it work is the Octopus/Tesla tariff, if you don't have a Tesla car. No standing charge and net metering with any deficit or surplus valued at 11 p/kWh. If you've got a very big PV system and are exporting most of it, the difference between 5p and 11p/kWh might hit the £500/year or so at which you can just about justify a Powerwall. It's worth noting the batteries in that scheme are managed remotely, so will form the sort of virtual power plant required to make batteries actually useful, as per @SteamyTea's comment above. That's reliant on a particular tariff being available for the next decade or more though...

[Matt60]

One option that I am researching is a thermal heat store with 3 internal emersion heaters which is also connected to solar thermal tubes. The latter should heat the majority of the thermal store during the summer, but I'd like to also link in a bottle fed gas fire with back boiler that would take over from the solar thermal and limit the amount of immersion heating required in the winter months.

 

Despite searching, does anyone know if you can buy a real flame, bottle fed gas fire with a back boiler?

Edited March 4, 2021 by Matt60

[Iceverge]

On 04/03/2021 at 21:24, Matt60 said:

One option that I am researching is a thermal heat store with 3 internal emersion heaters which is also connected to solar thermal tubes. The latter should heat the majority of the thermal store during the summer, but I'd like to also link in a bottle fed gas fire with back boiler that would take over from the solar thermal and limit the amount of immersion heating required in the winter months.

 

Despite searching, does anyone know if you can buy a real flame, bottle fed gas fire with a back boiler?

 

Solar thermal is parallel universe stuff at this stage. I really like the idea of it but I'm not sure I'd bother installing it if I got the equipment for free.  If you want solar hot water install PV and an immersion. Solar thermal has high heat losses from the panel to the tank, requires servicing, is less reliable and arguably more expensive at this stage. On top of that for most of the year it won't get the water hot enough or will get it too hot. 

 

There's a reason nobody uses back boiler gas fires. The cheapness reliability and ready availability of 90%+ efficiency gas boilers.

 

There's a simple answer to your issues here. Install UFH and a cylinder capable of using an ASHP.  Plan to run it on cheap electricity via Willis heaters and immersions initially with an option for ASHP later. 

 

Dedicate all your energy thinking about heating into making the house as low energy as possible. 

 

Do all your tinkering in the shed at some later date.