TerryE

There is possibly one thing worse than having an ASHP outside and the neighbours complaining about the noise. That's having it inside the house and all of the occupants complaining. In most weather conditions the temp drop across the ASHP air flow will be higher, maybe more like 5°C but the heat demand is also higher so the ASHP still needs to move tonnes of air per hour across the heat exchanger. You need large exchange areas and big slower fans to keep the noise down.

Thanks, IIRC the Planning Portal says that any ASHP installation can fall under Permitted Development if the installation complies with MCS 020 and part of this standard requires that the installation must be carried out by an MCS approved installer. Without a PD exemption, normal planning and building control applies. This is all a lot simpler if the installation is done as part of the initial build and part of this planning and building control approval, but in our case that was over 6 years ago. As a post sign-off install, this control itself introduces a shed load of bureaucracy and costs. In the case where the proposed ASHP is to the rear and within the property curtilage, you would need to demonstrate to BControl that the installation complies with gas-safe, positioning and noise regs. In this last case it would be practically impossible to get BC sign-off of your calcs unless the ASHP unit is an MCS approved model. BTW that Trianco unit has a heat output of 3 kW and a nominal power draw of under 1 kW.

Thanks. I've just checked BUS Property owner guidance, version 3 and you are right: to be eligible the ASHP must provide both space and water heating. The ASHP model and the installer must also be MCS certified. That's the big stumbling block for me. As I said in an earlier post I've already made our house "ASHP ready" during the build about 7 years ago. I really only need a small, say 3-5 kW unit with output flow at ~30°C driving direct into our warmslab or via a PHE. About the same amount of work that @JohnMo described above for adding DHW support. Maybe £3-4K work and bought-ins, if I did this myself and depending on what ASHP deal I could source. Entirely fit for purpose and just about achieving my 10 year payback constraint, but this would not achieve MCS certification and therefore this approach would not comply with Planning / Building Regs, so a no-no as far as I am concerned. The MCS installers that I talked to wouldn't touch this approach or some variant thereof with a barge pole. They'd want to rip our entire system our and based on the size of our 3 storey detached house, replace it with standard template based on something like a 11 kW ASHP, buffer tank, new UVC, etc. at maybe £15+K (OK, less BUS grant); all to save me maybe £400 p.a. Crazy.

First, since we have absolutely no intent of selling in the near future, this isn't really an issue for me. Next, I have a real issue with talking about monthly run rate as if it is the absolue goal. Surely we should be talking about LCoH from a consumption perspective. Our house is passive-class and has high thermal inertia. If some putative new owner simply switched to a timer based E7 tariff then the house would still be for more cosy than most new houses and it would still be very hard to make a proper payback case for installing and ASHP. Many members also seem to assert that using your ASHP for DWH is a must. Why? As I said in an earlier post on this topic we spend about £150 p.a. on water heating. Why go to all the hassle of extra buffer tanks, dual level ASHP control, dropping the overall CoP by maybe 20% just to save £100 a year (or even 3× that if we used a lot more HW): you have more kit to install, to have an annual maintenance contract and to discount the extra installation costs over the expected equipment life? The numbers just don't add up for us. Sorry. The SAP calc should not penalise any form of renewable heating solution. It should penalise fossil based heating solutions. Our's is not a typical mass build; it a passive-class house designed and built to a high spec. Actual performance is what should count in this scenario.

Remember we did our as-built EPC in 2017. The detailed stuff is back in the UK and not to hand, but IIRC we got marked down for using resistive heating and ended up with a C EPC, but still good enough to make BReg requirements. That being said, I regarded the whole SAP exercise as a paper one needed to get sign-off. What I really care about is real-world performance and total levelised cost of heating. Given that we use renewable electricity only, the total doesn't worry me and I suspect that going forward the scoring system will penalise fossil-fuel based heating more than direct electric.

We have an OSO UVC which is heated by dual immersion. I also have a couple of digital thermometers on the inner tank, one next to each immersion. My Node-RED heating control system does a day-ahead heating calcs at 23:00 GMT each night. We have Octopus Agile and the daily half-hour (HH) pricing runs 00:00 - 00:00 C.E.T. As far as DHW goes, the CH calc takes the average tank temp to work out a slight overestimate of kWh needed to bring it up to 55°C and this get scheduled at the cheapest HH slots with a cut out at 55°C (though at the mo the Immersion thermo cuts out first). We are on a Greek island ATM, so the HW draw is only from one occupant; our son who lives with us in his bed-sit on the 2nd floor. The screen capture below show the last 24hr history for Home Assistant. (BTW, the bottom scale is in local Greek time, sorry.) He hasn't used much hot water today (mainly just a quick shower, I guess). The OSO is really well insulated but even so most heating here is loss replacement. Checking my eventlog table, the total DHW heating used was 1.6 kWh costing 20p (The north sea is dead calm ATM, so the daily low price is quite high at about 13p.) Over the last few months since we commissioned the OSO it's been a lot windier and even though we use more HW with 3 of us in the house, the HH price for DHW has been averaging around 5p so we typically spend maybe 50p a day on DHW.

I have a passive-class house with a 70 tonne MBC "warm-slab" within the heated fabric of our build. I went for the deferred option of putting in the 6mm radial from the CU to an outside wall box and a insulated double pipe run from the UFH cupboard to where I would put the ASHP, but held off installing an ASHP and used a 3kW Willis as an interim means of heating the UFH loops so that we could size the ASHP based on a year or two run rate. The issue that we have is that going from using the Willis (plus Oil filled rad top up Dec/Jan) on an Octopus Agile optimised heating schedule to an ASHP at an average CoP of 3½ say might save us perhaps £300 p.a. in electricity costs. (We have a handful of days a year when we put in more than 30 kWh heat.) I'd want at least a 10 year payback so would want my install costs to be at most ~£3K. And then you have the issue that the typical life of an ASHP can be ~10 years. It's just easier to pay the extra £300. 6 years on, and I still can't make the investment case.

Ian, sorry to hear about the hip ops. Doing a self-build is body-damaging. My general health took a significant step down because of our build. I held it together until we moved in, but by then I'd used up all my reserves, and pretty much collapsed with exhaustion. Old age fighting slow recovery. Not sure which is winning. All I can say is that rest and recovery is more important than dotting i's and crossing t's.

Ian, I think that you are losing the plot. 🤣

This might be overkill for what you want, but this is what we did:

The point here is that the pavement is part of the public highway (if the way is adopted) and outside your curtilage, so it isn't your curb; it belongs to the local authority. The LA will typically retain active control on any works done to their highways. They will grant permission to do reasonable crossing works so long as the requester is willing to foot the bill, but they will want to cover admin costs, and limit execution of the work to one of their approved sub-contractors. That's just how it works. If you ignore the rules and do this work yourself, then you might get away with this, but you might also piss off the LA and be forced to foot the bill for any remediation work to restore to highway to its original condition.

Nope. We are in the "sustainable" core of our village and the planners like every new change to be sympathetic to the street scene. So PV on our street-facing roof (SSE aspect) was considered a no-no. There's no point in having an additional heat battery for us as our whole house intrinsically works as its own heat battery, but my thought is that this approach might be more appropriate for a retrofit or more traditional build-style. Any form of heat battery should allow you to time-shift heat generation and storage from periods where the unit price of electricity is low and decouple this from consumption demand.

Why should I care about some naff formula? I own my house outright and don't intend to sell it. Maybe the EPC version dated 2035 might be more relevant. It's our comfort and the actual running costs that are important to us.

A 1,000 ltr tote buried in hole in the garden wrapped in say 400mm EPS 100 storing water at 60°C would leak heat at about 50W. If you don't want to "waste" that heat, then stick a greenhouse or shed on top. This should be good to store around 40 kWh heat for dumping into UFH. Just an off the wall idea.

Yup. We are of an age where we are facing that. It's what life does.