Bivalent ASHP and oil boiler

greenbee

Our oil tank is far too small for the house, and due to the position, replacement with a larger tank is likely to be impossible. Because the tank is only 1000 litres (5 bed house, approx 3000 square feet, EPC C (72) and could probably do with more loft insulation), and minimum order is 500l I have to wait until the watchman is showing at least half empty to place an order - and because the delivery is always ‘on or before’ I can’t make assumptions about the level dropping (on occasions I’ve assumed it will be 2 weeks, allowed for extra, and then not had space), so at this time of year, particularly with the recent cold snap, poor controls (due for replacement) and workmen in and out it is a bit stressful. I think I’ll make it to the delivery due ‘on or before’ Monday - but who knows as I have no date/time as yet.

That’s a rather long-winded lead-up to asking for opinions on adding an ASHP to create a bivalent system (oil boiler is a Grant, running well, not yet in need of replacement) to reduce dependence on oil. And reduce stress! We plan to install solar PV with a combine battery and inverter as soon as possible in the NY, so feel it makes sense to do this at the same time if possible, but we don’t know much more about it than Google can tell us!

FreeBear

It is possible to combine multiple heat sources to run a wet central heating system. A thermal store with multiple coils is one way if you have space for another big tank of water. Alternatively, a small heat exchanger along with some fancy valves & control system.

Grant have a blog post that might provide some answers for a hybrid system - https://www.grantuk.com/knowledge-hub/tips-advice/maximising-the-benefits-of-combined-heating-technologies/

lohr500

I am sure it is possible, but as far as I am aware you wouldn't qualify for the ASHP grant if that was part of your thinking. 

matelodave

A ssaid above, you'd need to check the qualifications for a grant if you want bivalent - you might have to install a heat monitoring system to enable you to establish how much heat your heatpump generates. 

It was probably easier in the RHI days when you could get paid for what you produced but that required a heat meter, I doubt that an upfront grant would do it nowadays.

Personally I'd go all or nothing, (eg heatpump OR oil, not both ) but you'd have to do some very carful sums to work out what would be best.

Although it may seem like a good idea it's probably not worth the hassle and cost. However that said, if you do decide to explore it, please keep the thread going so we can all benefit from your explorations as it's the best way to share info and increase our collective knowledge.

Heatpumps are still a bit of a black art and info sharing is the best way for us all to understand how to use them properly and efficiently

greenbee

Thanks all - i'm not looking for a grant, nor am I planning on replacing all the radiators and pipework as a. the ground floor pipework is buried in the floor (fine for the UFH, which will work with an ASHP, but not for the rads) and b. I work from home and need to be able to continue to do so to earn a living and pay for it - the disruption from redoing the pipework and taking up all the floorboards upstairs plus the downstairs floors would be too much (my last house was a major renovation - I know what I can tolerate and not be fired). However any rads or pipework that are replaced in future will be done with lower flow temps in mind. 

For now, I just want to put a solution in place that will resolve the fuel insecurity of such a stupidly under-sized oil tank and potentially allow a switch-over at some unspecified point in the future (hence not necessarily wanting to replace a perfectly well-functioning boiler with a hybrid system). 

Looking at the blog that @FreeBear linked to, it seems that solar thermal might also be worth considering - we had this when I was a child, and it seems to have gone out of favour but I remember my dad saying that on sunny days it provided most of our HW needs, and on less sunny days significantly reduced oil consumption as the water being heated was so much warmer. 

The first job is clearly better heating controls, and I hope to get those done as early as possible in the NY. The watchman is currently flicking between 3 bars and 2 (the point at which I get nervous), and on this one the refill symbol comes on at 2, whereas on my old one it came on at 1. It was on 1 when we moved in, but that was in August, so it was easy enough to switch the boiler off and use the immersion on for HW as needed. (which reminds me, I need to add putting a timer on the immersion to the endless list for the electrician!). 

Reed_Richards

Solar energy will never heat an ordinary house in winter; ask yourself why it is cold in winter if you doubt this.

You can certainly buy heat pumps that will function as part of a hybrid system in conjunction with an oil boiler.  But you might find that the way this works is that you use mostly the oil boiler in winter and mostly the heat pump the rest of the time so your security of oil supply issue is not much improved.

matelodave

Not sure if getting a smaller heat pump to supplement an oil boiler and then getting a bigger one at a later date to replace the oil boiler could be considered cost effective, but in the end its up to you

QrizB

greenbee said:

For now, I just want to put a solution in place that will resolve the fuel insecurity of such a stupidly under-sized oil tank and potentially allow a switch-over at some unspecified point in the future (hence not necessarily wanting to replace a perfectly well-functioning boiler with a hybrid system).

If you don't mind being a bit Tom & Barbara, you can deal with fuel insecurity with a couple of these and one of these. And some hose.

FreeBear

QrizB said:

greenbee said:

For now, I just want to put a solution in place that will resolve the fuel insecurity of such a stupidly under-sized oil tank and potentially allow a switch-over at some unspecified point in the future (hence not necessarily wanting to replace a perfectly well-functioning boiler with a hybrid system).

If you don't mind being a bit Tom & Barbara, you can deal with fuel insecurity with a couple of these and one of these. And some hose.

For another £15, a 1000l IBC would be more effective. Unlikely to comply with current regulations for fuel storage though.

greenbee

FreeBear said:

QrizB said:

greenbee said:

For now, I just want to put a solution in place that will resolve the fuel insecurity of such a stupidly under-sized oil tank and potentially allow a switch-over at some unspecified point in the future (hence not necessarily wanting to replace a perfectly well-functioning boiler with a hybrid system).

If you don't mind being a bit Tom & Barbara, you can deal with fuel insecurity with a couple of these and one of these. And some hose.

For another £15, a 1000l IBC would be more effective. Unlikely to comply with current regulations for fuel storage though.

I did wonder about daisy-chaining tanks but apparently that’s not a good idea either 😉

I have a friend coming over today who restores historic buildings and has installed all sorts of different types of heating systems from traditional to cutting edge, so will get their input. Nothing is perfect, but I’m sure we’ll find a solution. 

Solar is a no-brainer as we have a lot of very usable roof, and setting up EPS means not having to worry about working when the power goes out. We don’t use a huge amount of electricity, and will use less when the lighting is sorted out so we don’t have 23 inset LEDs on every time we go into the kitchen!

i’m pretty sure that sorting out the controls will help with consumption too - particularly as the ground floor heating currently kicks in when it feels like it, regardless of whether the thermostat is calling for heat. 

Clearly I have a bit of time for research as nothing is going to be done over the holidays. And I have 600l of oil arriving on Monday.

Reed_Richards

greenbee said:

Solar is a no-brainer as we have a lot of very usable roof, and setting up EPS means not having to worry about working when the power goes out. We don’t use a huge amount of electricity, and will use less when the lighting is sorted out so we don’t have 23 inset LEDs on every time we go into the kitchen!

That low electricity usage is only for as long as you don't have an ASHP.  One of those will greatly increase your electricity usage and you will have to turn it off in the event of a power outage (or exclude it from your EPS) or it will quickly drain your battery storage capacity when it is active.

Don't you need dark glasses in the kitchen?