Ecodan advice - hybrid

[newbuild upnorth]

we will be fitting an Ecodan ASHP in our new build, probably a 8.5kw maybe a 6kw, the calcs and things have not been finally done yet, we will be using a Mitsubishi as they are the best supported up here and seem to be the preferred choice, its also the type the company we will be using supply and repair.

 

I have a few questions for anyone with experience or have maybe been down this route before.

 

while reading on line about them I see the Ecodans have some sort of hybrid function built in for integrating with existing oil or gas boilers, anyone know how this is done? I can't see any info on this.

 

secondly, if I were to opt for a 250 / 300 litre ecodan solar cylinder which has a secondary coil fitted, is there anything stopping me from running an oil boiler through this coil? as far as I can gather this would only give me DHW heating as since the ecodan pre plumbed tanks use a heat exchanger for the DHW there would be no way to use this coil for the UFH side of things.

 

thirdly! if I were to use a buffer tank inline with the ASHP, im imagining only on the return side? and I then connect the boiler to the buffer tank to heat the primary water will the ASHP and UFH system just run as normal but just not have to heat the water or would it get all confused, ie the house is calling for heat so the pumps would run but the ASHP wouldn't have to heat the water being returned to it as it would already be preheated by the boiler.

 

my ideal solution in my mind is a 100liter buffer tank with an indirect coil, with 1 1/4 fittings and I just run the boiler through the coil and the ASHP on the other section and the two systems are separated, but I can't see anything like that online, the closest seems to be just a standard indirect unvented cylinder but these have 28mm on the coil and then 22mm on the HW side??

 

any experience or insights appreciated.

[JohnMo]

Having experimented with just about every configuration. A hybrid will cost you more to run.

 

Just about every heat pump will support a hybrid solution. But the bottom line is you don't need them. But they only ask for the additional boiler to start if the heat pump cannot cope, so is undersized for the duty. If you are asking the heat pump for 30 Deg flow and the heat pump is doing that it will not ask for the boiler assistance. 

 

1 hour ago, newbuild upnorth said:

buffer tank inline with the ASHP, im imagining only on the return side?

So a volumiser. With UFH a volumiser isn't generally needed, you are just adding extra costs.

 

So hybrid solution would consist of

Another boiler and oil tank, all associated materials, spend that money on solar and or battery.

 

 

KISS. One zone, all UFH loops on or off, NO mixer or additional pump on manifold. Run from the manufacturer controller only, NO third party controls, run on weather compensation. Or instead of pure weather compensation, a slightly oversized heat pump, set up weather compensation and use the second operating point to run hotter when there is excess PV generation, and or during cheap tariff periods. This will reduce bills by quite a margin.

 

Make sure your heat pump can do cooling, adds flexibility you may need or like it.

[newbuild upnorth]

Thanks for your reply, its not so much about the cost saving, its a newbuild in shetland, in winter theres regular short powercuts with storms and snow where i am and with my current oil boiler i can just run it as normal with a small generator, 

perhaps an unpopular opinion but im not so interested in the green credo of ASHPs, if id had the option id have just put in another oil boiler in the new house, with the coldest climate in uk and the highest electricity costs i am hard convinced that an ASHP makes sense but i have to so i just need to find a reliable means to back it up.

 

how did you interface a boiler with and ASHP, do you think i could just heat the primary fluid in a buffer tank? 

[JohnMo]

We are NE Scotland, so milder than you, but still get -9 most years where we are and more than our fair share of power cuts.

 

We have a 6kW heat pump, and it runs a small generator (7.9kW) and you can cook your tea at the same time. So house runs pretty much as normal.

 

But now have the generation as a secondary standby. Have a GivEnergy AIO battery, 13.4kW usable storage capacity, charge it up on E7 it will run the house on all but the coldest days until next recharge.

 

Hybrid plumbing can be done in several ways.

You can run in parallel, just tee in to the ASHP flow and return, you can run in series, so all water always flows though the boiler. I had mine (decommissioned last week) via a plate heat exchanger. All depends on your house and heating system layout.

 

I found the generic control system in the heat pump pretty rubbish, so in the end did my own.

 

Used a good UFH controller with outdoor weather sensor and a timed average outside temp to initiate a heating demand. Controller only used to start stop boiler and monitor room temperature, hall sensor used for control. Used a +0 and -0.1 room sensor to control the heating demand, this went to the boiler via the UFH controller. Boiler flow set higher than WC curve on the ASHP. Setup boiler so once started it ran without stopping (a fixed flow temp on weather compensation curve and set back function). The ASHP would switch off as it saw the return temp satisfied.

 

Boiler min output was about 7 to 8kW. No buffer or volumiser required.

 

Have a read

https://forum.buildhub.org.uk/topic/41531-boiler-heat-pump-hybrids/

[newbuild upnorth]

That is very interesting, so I could just run the ASHP through a PHE, probably on the flow side and put the boiler on the other side of the PHE presumably with a small volumiser on the boiler circuit.

im just surmising here but as you say if the ASHP sees adequate return temp it won't be required but the other controls would work as if the boiler wasn't there.

I wouldn't expect a fair sized PHE would add much restriction to the flow.

 

thanks for the info, ill have a bit of a look into that

[JohnMo]

3 hours ago, newbuild upnorth said:

PHE

Or even easier and cheaper a close coupled tee. So on the ASHP pipe, take suction tee to boiler and return to a tee very close to the first. This would give complete hydraulic separation and let you boiler pump run as it needs. But ideally you would match ASHP flow and boiler flow to be pretty close to each other.

 

It would look similar to the attached, but the pump would not be needed. Assuming the oil boiler has one.

 

 

Question can you get an oil boiler that does weather compensation and will run priority demand hot water? If you can't this may get messy. An oil boiler may demand mixers on the UFH.

 

Or you do a 2 port buffer, they are more efficient than the normal 4 port but the whole control scheme changes.

 

2 port buffer temp is the only thing that starts and stops the heat source, house temperature. So ASHP or boiler would fire to manage the buffer temperature. You do a simple electrical change over switch or control on outside temperature to switch over or a combination of the two fire power outages. The central heating side just activates the secondary circuit circulation pump. To do this you are better to use a small hysterisis room thermostat in say the hall, run a fixed temperature on heat pump, say 35 degrees and similar on the oil boiler. Then you need to think of DHW heating - ASHP will priority demand so run two flow temps one for heating and one for DHW. Your boiler?

 

You need to start reading mitsubishi manual to see what it shows and understand what it does first.

 

New build well insulated on MVHR heat demand is very low, an oil boiler doesn't modulate well, if at all. So you will need the smallest boiler you can get. Or a huge buffer.

[Dillsue]

Whether you have back up heating or not is entirely down to individual circumstances. Unless someone's in the same circumstances their needs/wants are unlikely to be the same as yours.

 

A heat pump requires a fairly beefy supply and would need a beefy generator to keep it running, an oil/lpg boiler wouldn't so a small generator and a few gallons of fuel will keep the heating and lights running for days. If there's a major storm which are likely to get more frequent and youre on a remote supply then you could be off grid for days which a typical battery bank won't cover. If your in an urban area sharing a supply with 1000s of others you'll be top priority for repairs to get you back on supply. If you're remote and share a supply with few other houses you'll be lowest priority to get back on supply. That's how the DNOs prioritise things when dealing with widespread storm damage. 

 

I don't know how the Ecodan interfaces to a back up boiler but the Therma V that I'm installing just now provides a volt free contact to enable a backup boiler to run. The configuration seems to allow the outdoor temperature value to be set that shuts the heat pump down and activates the boiler contact.....the manual isn't the best written but that seems to be what it says??

[JohnMo]

51 minutes ago, Dillsue said:

heat pump requires a fairly beefy supply and would need a beefy generator

No it doesn't for a new build house, a 7.9kW geny isn't big. It will allow heat pump to start stop and run while the hob is on cooking the tea. Any Watts excess can go into the battery.

 

I would really just install a room sealed log stove for belts and braces secondary heating. No power needed at all and house heating sorted. And have a back up generator, to run heat pump and house if you want.

[newbuild upnorth]

that's also interesting, it looks like ecodan FTC6 and FTC7 controllers on a pre plumbed tank already have boiler hybrid function built in, ill do a bit more research but looks like the header even has blanked connections ready for it.

 

[newbuild upnorth]

5 hours ago, Dillsue said:

Whether you have back up heating or not is entirely down to individual circumstances. Unless someone's in the same circumstances their needs/wants are unlikely to be the same as yours.

 

A heat pump requires a fairly beefy supply and would need a beefy generator to keep it running, an oil/lpg boiler wouldn't so a small generator and a few gallons of fuel will keep the heating and lights running for days. If there's a major storm which are likely to get more frequent and youre on a remote supply then you could be off grid for days which a typical battery bank won't cover. If your in an urban area sharing a supply with 1000s of others you'll be top priority for repairs to get you back on supply. If you're remote and share a supply with few other houses you'll be lowest priority to get back on supply. That's how the DNOs prioritise things when dealing with widespread storm damage. 

 

I don't know how the Ecodan interfaces to a back up boiler but the Therma V that I'm installing just now provides a volt free contact to enable a backup boiler to run. The configuration seems to allow the outdoor temperature value to be set that shuts the heat pump down and activates the boiler contact.....the manual isn't the best written but that seems to be what it says??

 

you're absolutely right there, we get our share of power cuts in the winter and as hard as they try they can't get it restored quickly if the poles are down, and they have to prioritise the population centres and get the most people back on first. 

that's not us unfortunately and even last winter we were completely off for 4 days in one go, that's my motivation really, we were not as prepared as some but with a 4kva generator we could pretty much operate as normal, lights, heating, microwave.

if im going to the effort of a new house id like the same kind of security, it will have to be done after the fact but id like to make as much preparations for it while I install my ashp and tank.

[Dillsue]

6 hours ago, JohnMo said:

No it doesn't for a new build house, a 7.9kW geny isn't big. It will allow heat pump to start stop and run while the hob is on cooking the tea. Any Watts excess can go into the battery.

Maybe not for you but our 2.2kw honda unit is as much as I'd want to carry around when the lights go out. A backup heat source other than the HP also covers you for heat pump failure.

 

[JohnMo]

2 minutes ago, Dillsue said:

Maybe not for you but our 2.2kw honda unit is as much as I'd want to carry around when the lights go out. A backup heat source other than the HP also covers you for heat pump failure.

 

It's on wheels, pull out of shed, use proper extension to plug into house (external socket), flick the change over relay, full house has power.

 

£700 for geny, £50 for changeover switch, lots cheaper than an oil boiler, tank etc.

 

7 minutes ago, Dillsue said:

backup heat source other than the HP also covers you for heat pump failure.

Log stove?

[Dillsue]

1 hour ago, newbuild upnorth said:

 

you're absolutely right there, we get our share of power cuts in the winter and as hard as they try they can't get it restored quickly if the poles are down, and they have to prioritise the population centres and get the most people back on first. 

that's not us unfortunately and even last winter we were completely off for 4 days in one go, that's my motivation really, we were not as prepared as some but with a 4kva generator we could pretty much operate as normal, lights, heating, microwave.

Your 4 days trumps the max 3 days we've been without power. That 3 days was over Xmas a long time ago but it leaves a legacy of us always having a backup for essentials.

[Dillsue]

5 minutes ago, JohnMo said:

It's on wheels, pull out of shed, use proper extension to plug into house (external socket), flick the change over relay, full house has power.

 

£700 for geny, £50 for changeover switch, lots cheaper than an oil boiler, tank etc.

 

Log stove?

I'd guess as a backup for a failed HP a log stove with fireplace/chimney/flue/wood store/logs/back boiler etc isn't gonna be any cheaper than a boiler and oil tank/propane bottle?? Needing only a small genny to run either means another few hundred £ saved to use a boiler or WBS also as a back up for a power cut rather than a larger genny to run the HP.

[JohnMo]

So back to topic - topic says hybrid, but the reality isn't that, it's a secondary heat source, which is very different.

 

So in a power cut, you need the heat pump off, or it will try to start up. A hybrid system uses the ASHP primary circulation pump. That will not be available.

 

The secondary heat source needs to have full autonomy to heat without ASHP being powered and using it's circulation pump. In hybrid mode, no ASHP power, no heating.

 

So you need hydraulic separation for ASHP and boiler. And either needs to provide heating circulation and DHW heating. It starts to grow arms and legs complexity wise if you are not careful. Or you install a buffer and take an efficiency hit every day. But that doesn't address DHW in a power cut.

 

@newbuild upnorth you to write down step be step what you really need to achieve. What resources you will have available. Then work through how to achieve it. Hybrid running will not provide heating in a power cut with a small generator.

[newbuild upnorth]

7 hours ago, JohnMo said:

So back to topic - topic says hybrid, but the reality isn't that, it's a secondary heat source, which is very different.

 

So in a power cut, you need the heat pump off, or it will try to start up. A hybrid system uses the ASHP primary circulation pump. That will not be available.

 

The secondary heat source needs to have full autonomy to heat without ASHP being powered and using it's circulation pump. In hybrid mode, no ASHP power, no heating.

 

So you need hydraulic separation for ASHP and boiler. And either needs to provide heating circulation and DHW heating. It starts to grow arms and legs complexity wise if you are not careful. Or you install a buffer and take an efficiency hit every day. But that doesn't address DHW in a power cut.

 

@newbuild upnorth you to write down step be step what you really need to achieve. What resources you will have available. Then work through how to achieve it. Hybrid running will not provide heating in a power cut with a small generator.

JohnMo thanks.

 

ive no experience of ASHP so I dont know where a secondary becomes a hybrid or a hybrid becomes a backup.

I've read a lot on ecodan ftc6 and ftc7 in the last couple of days and it references hybrid in the context of adding and controlling a second heat source - both boilers and electrical heaters.

 

from what ive read the ecodan when combined with the ecodan pre plumbed cylinder can be used in a hybrid mode where it controls a boiler if selected as priority, not sure quite how but it looks simple on the drawings, and also if hybrid mode is selected and it knows there is a boiler connected you can go into an emergency mode where the ASHP isn't available or comms are lost or for instance a power loss and it uses the boiler for heat - provided there is enough power for all of that.

 

as far as I can see everything else works as if the heat pump is there, primary pump, controls, everything.

 

this has encouraged me a bit now, be nice to see it done in practice or talk to someone who has done it with an ecodan but it all seems to be possible.

 

incase anyone else comes looking for the same -

 

 

Hybrid P-P, 2x HTG Zones.pdf

[JohnMo]

From the looks of the drawing the cylinder has a low loss headers (a small capacity buffer) which takes the flow from boiler and heat pump. So both heat pump, boiler and heating circuits are hydraulically separated. So a good start, but like a buffer you will take an efficiency hit and you have multiple pumps.

 

The "but", I have experimented with my ASHP, using the inbuilt hybrid mode, the way the logic works it's looking for a target flow temperature within a given tiime. If that conditions is not met, the second heat source is activated.

 

This is where you may need to speak to manufacturer.

 

From what I've seen, when you start your generator the ASHP will see power, so will assume it has enough power to do what it does and it will try to start, because everything is fit and healthy, as far as its concerned. It will trip a small generator on overload. If you go outside and manually isolate the outdoor unit, obviously when you start your generator the ASHP cannot start, but the FTC6 unit on the cylinder has some hefty loads as well, it also has a 24v signal from the outdoor unit (which is switched off). So will you have a permissive for anything to start? I have no clue, this where you need input from manufacturer.

 

Are you looking to get a grant for the ASHP, anything seen as hybrid, is excluded from the grant scheme 

[newbuild upnorth]

there's no grants available for new builds now so the basically mandatory ASHP for planning up our way stings even more.

 

ill keep searching the internet for ecodan info, Mitsubishi offer basic information to everyone but hopefully more detailed info to agents and installers.

the emergency mode seems to overcome the ASHP availability issue, it overrides the comms to the ASHP and assumes its unavailable, this is where I expect ill need to physically try it or get a meter on a similar unit.

[Dillsue]

An option to resolve all your queries would be to get a secondhand unit and play with it then either use it yourself or resell as a proven working unit. Ours is secondhand and I hooked it up to a 45 gallon drum of water to confirm it worked. Not sure what options you've got in Shetland but you can pickup HPs with controllers for a few hundred £. Maybe your installer would have a unit you could borrow?? Ours had been removed because the new householder didn't like it in their small garden and the installer who removed it and refitted a gas boiler wanted shut of it.