Home made Hybrid Oil and ASHP

[Fly100]

Hello all,

 

Id appreciate your toughts on the following.

 

We will be changing our car soon to a Plug in Hybrid which will enable us to make use of a 4.5p per unit electricty through the night.With this in mind im looking to install an ASHP in addition to the exsisting oil boiler for use in the colder months. House is a selfbuild 3 years old with underfloor downstaris and rads upstairs (oversized rads for future proof).

All the above world allow me to run the ASHP for 5 hours through the night for a small amount of money. Going on from that is how to merge the 2 sytems? I have 2 spare ports on my buffer vessel so the plumbing part is easy, its the control methods that I fall down on.

Has anyone completed such a task ?

 

Thanks,

Fly

[JohnMo]

Daikin do a hybrid solution.  They do two versions, a split and mono block.  You need the mono block version.  Basically you can have their solution of ASHP and gas boiler, or their ASHP and any other boiler.  The heat pump does heating only.  You boiler does hot water and or heating.

 

Think Vaillant and others also do a similar solution.

 

The heating system will run in bivalent mode, for heating which is either or not both together.

[joth]

Not a specific recommendation, but as another datapoint the Ecodan supports this out of the box in the standard controller too.

Search the FTC6 install manual for "boiler" for schematics and setup instructions (Dip switch SW 1-1, inputs IN4 & IN5, output OUT10, thermistors THWB1 THW10)

 

https://library.mitsubishielectric.co.uk/pdf/book/Ecodan_FTC6_PAC-IF071-3B-E_Installation_Manual_BH79D843H03

[Wil]

The cool energy ASHPs have a contact pair that allow you to choose a time to bring in a backup heating source. You run the ASHP as lead until it decides it can't cope and then bring the Oil burner in behind it. You could also use the ASHP to 'pre heat' the water going into the oil burner so that it doesn't have to work so hard but I have no idea of the efficiencies and was persuaded to just drop the oil burner altogether and run the ASHPs only.

 

If you've already oversized the rads, you could run the oil burner at a really low temp too.

 

It's a tough combo and would need a bit of fettling to run an ASHP in parallel with an existing Oil burner rather than buy a hybrid.

[JamesPa]

You could crudely just switch between the two so you use oil on the coldest days and ASHP on the warmer days (or ASHP at night and Oil during the colder days).  A couple of three way valves and either a manual switchover or one which is somehow temperature-controlled would do this.  Essentially arranging the plumbing such that either the oil is connected or the ASHP is connected but never the two together.  Not as efficient but far less complicated.  Im thinking about doing exactly this (in preference to anything complex/expensive involving buffer tanks etc) so that I can retain my existing gas boiler as a backup to the ASHP I intend to install, just to cover failures.

 

Bear in mind that the ASHP might take some time for the compressor to 'warm up' though (see the thread about ecodan standby consumption to understand why).   

[burtlad]

We currently have an ashp, its been installed about 6 years, so the rhi payments will soon be coming to an end after 7 years.

We already have a 12kw solar system, with Eddi water heating with surplus, I'm going to add another 8kw of pv in the next few weeks but in winter months this still is no where near enough especially during the night and early hours when most the power is needed.

 

I'm contemplating adding in a gas or oil boiler to help the system when it's really cold, as the house struggles to get up to temperature when weather is consistently below a couple of degrees.

The other winter our electricity bill was over £1000 for one month, with the log burner on at every opportunity, so it feels like burning money maybe a cheaper way to stay warm.

 

If adding a small combi boiler to the system for use in colder temperatures, say below 5 degrees, is it best to feed hot water directly into the system, or would it be more efficient to pre heat the air going into the ashp?

I was thinking this could be done with a simple arrangement of large vehicle radiators (heat exchanger) in front of the heat pump heat exchanger.

 

My thought was this would stop the constant defrost cycle being required but the rest of the system could operate as normal, and if over the preset temp would just pull ambient air through this new primary heat exchanger.

 

The existing system would not need any reconfiguration or change over and the new fossil fuel element would not be critical but a boost.

 

At a later date if this worked the hot water side of the system could have some direct input during these periods, when the solar and Eddi unit is not helping us out.

 

If anyone has any experience or thoughts on this it would be appreciated.

 

Similarly if anyone can recommend any trend systems that on a sunny day with cold night ahead could harvest any spare energy? I've read thermal stores or buffer tanks are not recommended for ashp applications. Our existing ashp controller is a fairly basic samsung model with very limited Integration.

 

Next on my list is a small hydro electric setup, but this will take a little more work!🤔

[Conor]

5 minutes ago, burtlad said:

We currently have an ashp, its been installed about 6 years, so the rhi payments will soon be coming to an end after 7 years.

We already have a 12kw solar system, with Eddi water heating with surplus, I'm going to add another 8kw of pv in the next few weeks but in winter months this still is no where near enough especially during the night and early hours when most the power is needed.

 

I'm contemplating adding in a gas or oil boiler to help the system when it's really cold, as the house struggles to get up to temperature when weather is consistently below a couple of degrees.

The other winter our electricity bill was over £1000 for one month, with the log burner on at every opportunity, so it feels like burning money maybe a cheaper way to stay warm.

 

If adding a small combi boiler to the system for use in colder temperatures, say below 5 degrees, is it best to feed hot water directly into the system, or would it be more efficient to pre heat the air going into the ashp?

I was thinking this could be done with a simple arrangement of large vehicle radiators (heat exchanger) in front of the heat pump heat exchanger.

 

My thought was this would stop the constant defrost cycle being required but the rest of the system could operate as normal, and if over the preset temp would just pull ambient air through this new primary heat exchanger.

 

The existing system would not need any reconfiguration or change over and the new fossil fuel element would not be critical but a boost.

 

At a later date if this worked the hot water side of the system could have some direct input during these periods, when the solar and Eddi unit is not helping us out.

 

If anyone has any experience or thoughts on this it would be appreciated.

 

Similarly if anyone can recommend any trend systems that on a sunny day with cold night ahead could harvest any spare energy? I've read thermal stores or buffer tanks are not recommended for ashp applications. Our existing ashp controller is a fairly basic samsung model with very limited Integration.

 

Next on my list is a small hydro electric setup, but this will take a little more work!🤔

I think your problem is insulation, or rather lack of. Details please.

 

You seem to be using up to 100kWh of electric in a day?! No matter what your heating source, it'll be expensive. 

 

[ProDave]

With 12kW of solar and planning to add another 8, that will be 20kW.  To sensibly self use all of that you need battery storage. I hope that is in your plan.

 

As already noted the issue is for some reason your house needs a lot of heat.  What size is your ASHP and what did the heat loss calculations before deciding what size ASHP say?  And how is the heat delivered?  Radiators or UFH.

 

£1000 per month electricity bill would make me sit up and think where can I better spend £1000?  Lots more insulation perhaps?

[JohnMo]

I would strongly suspect a lot of your issues are related to setup and operating. Rather than anything else. Would bet your immersions are doing a lot of the work instead of the ASHP. 

 

Tell us more on your set up and how you operate it? Weather compensation continuously, thermostat(s) and set temperature, on and off via a timer. UFH, radiators or a mix, buffer or no buffer etc etc 

 

Doing a hybrid set up is pretty straightforward.

 

Radiators in front of the ASHP, sound like a lot of energy in (gas or oil) and not a lot of gain in heating energy.

 

 

[sharpener]

2 hours ago, burtlad said:

would it be more efficient to pre heat the air going into the ashp?

I was thinking this could be done with a simple arrangement of large vehicle radiators (heat exchanger) in front of the heat pump heat exchanger.

 

Interesting idea but I think a lot of the heat would not be captured by the HP and wasted.

 

As others have said it sounds as though there is something seriously non-optimal about your setup which needs identifying and fixing first.

 

2 hours ago, burtlad said:

I've read thermal stores or buffer tanks are not recommended for ashp applications. Our existing ashp controller is a fairly basic samsung model with very limited Integration.

 

Buffer tanks reduce thermodynamic efficiency due to mixing and are to be avoided as they reduce CoP, though are necessary in some circs. If you need more volume for defrosting then configuring it in the return line as a volumiser is better.

 

Thermal stores are fine. I have got a 270 litre TS which will hold up to 10kWh of usable heat. It gets charged up during off-peak rates (to a temp set by its own WC coefficient), and then discharged through the bedroom rads before we get up. It is early days as the heating season has barely started but indications are it is working as intended.

 

If Octopus succeed in finally installing a smart meter next week I will be able to switch to their Cosy tariff so I will get a second bite of the cherry 1300 - 1600. The third period 2200 - 2400 is not a lot of use for directly charging the TS, but will enable me to run the bedroom rads cheaply in real time so I can instead use the TS to heat the living room during the expensive period 1600 - 1900. The house is long and thin so heating it all 24/7 except when we have visitors makes little sense.

 

As @ProDave says, you should think about battery storage as well, we have 10kWh of that in addition. After taking account of the CoP the initial cost/kWh is broadly the same as a TS but deteriorates slowly in use and the eventual life is a lot less, so the two forms of storage are complementary.

[PhilT]

2 hours ago, burtlad said:

 the house struggles to get up to temperature

To what temp are allowing your rooms to drop? I never allow mine to go below 18, max 21, on 24/7

[SteamyTea]

Can you not add in a secondary heat pump, maybe some simple A2A ones.

 

I run my whole house of about £600 of electricity, a year.

 

Have you looked at your half hourly usage date from your smart meter?

[IGP]

As others have said, something doesn’t sound right to have those kind of bills and still be a bit cold unless you genuinely have an uninsulated mansion.