Micro CHP boiler - Baxi Ecogen or similar experiences/recommendations?

[readiescards]

Still looking at living off-mains electric grid.  

Will have LPG for heating & cooking.  

 

Anyone experience of the Baxi Ecogen or SenerTec Dachs mini-CHP or any other boiler with electric generation recommendations?

 

 

[Nickfromwales]

I've had a good read tbh and it's a tough one to call, because of your particular circumstances ( off grid ). 
As I'm quite familiar with your 'case' I'm privy to the fact that you'll have a sizeable ( non MCS ) Pv array, and that you are considering a chunky generator plus battery bank.  
As im 100% unfamiliar with this technology I'm on as steep a a learning curve as you are btw, so, I'm asking the questions as much as answering them

The links.  

The ecogen

The Dachs ( Sener Tec ) unit

 

The Baxi unit is a combi, and only a 24kw combi, so at first glance doesn't really seem to be a contender for your property due to dhw production constraints. As producing instant dhw in any reasonable capacity is going to be non-sympathetic to your situation I'm pretty sure the Baxi can be discounted from this equation unless you see LPG providing a lot of the space heating where you could just ignore the dhw side, make that off to a local hot outlet ( kitchen sink / utility would be ideal but any hot outlet would do ), and zone valve the heating output to split between space heating and heating of the dhw cylinder/s. That would bring it back onto the list of 'possibilities', but one major upside is it's got a very low modulation rate @ circa 3kw. At that low output both the electrical output levels and the boiler efficiency would suffer, so again a complete bar steward to get this through without highlighting pros and cons a plenty. 

 

Next is the Dachs unit. A quote from Page 38.......

 

"The Dachs is a micro CHP system to cover heating, electricity and domestic hot water demand. The output, reliability and functionality is suitable for small buildings with high heat demand as well as for commercial, office, public and multi-apartment buildings.
The Dachs can operate as a single unit as well as in a multi-module system with up to 10 modules. Each Dachs unit can provide 5.5 kW electrical and up to 14.7 kW thermal (with condensing unit)."

 

As you can't export excess electrical generation and CHP isn't eligible to claim RHI, you'll either need to be able to consume it, store it ( batteries ), or, most importantly, ensure that you've not spent too much money on producing it in the first place.

The benefit of a simple generator over the CHP is that you can run the genny without having the issue of what to do with the produced heat i.e. you can run the genny in the summer without worrying about excess heat energy production. The benefit with the genny is that a water-cooled one can provide heat energy which can be gleaned for consumption ( via a TS ) and given the genny will most likely be used in the colder / darker ( little or no Pv generation ) months of the year, the heat energy created will largely be consumed by the property ( as it can charge the proposed large primary ( seasonal ) TS, the heating and dhw preheat TS and the UVC as heat batteries ) whilst the electricity produced is charging batteries and offsetting the immediate electrical demand. 

The only way to run the CHP for electricity is to store the bi-product ( heat ) as thermal energy in a huge TS, but that'll soon max out and the boiler will then go into standby. Then, if you don't use that heat energy it's been wasted as it'll be lost as the latent heat ebbs from the TS. 

From a glance, it seems that the Dachs is only really beneficial if your burning gas for any meaningful time during any 24hr period. With a well insulated, reasonably airtight house with low temp space heating ( Ufh ) and MVHR, your situation doesn't really match the criteria that these units are intended for. That coupled with no incentive schemes, in your individual case, plus the high capital cost makes them an unwise choice IMHO.

So simple. 

[readiescards]

Thanks Nick, just had a chat with a guy at Baxi.  Apparently the Dachs needs mains electric.  While the Ecogen is currently being replaced (he's gone away to find out when).

 

If you get a moment have a look at this:

 Youtube: How it works Ecogen

 

I actually thought if could use the Ecogen in low mode (i.e. without the supplmentary heater exchanger running) it could nicely tick over keeping the heat for the UFH topped up whilst keeping the batteries topped up.  I did not see the Ecogen as a replacement for the backup genny just a way of getting something for nothing (though the costs (£3700 + installation) might mean it's another 100 year payback jobbie!)

 

 

 

[Nickfromwales]

Something for nothing ? 

The video about the Innotech which produced Hydrogen from natural gas is quite interesting, but he stumbled a bit when mentioning that biomass may end up producing the electricity required to support the conversion process 

Still makes me wonder where the Hydrogen will come from when the gas runs out / is too expensive!

Thanks for the video link, I was too knackered the weekend to think of something so simple. Now I realise the ecogen isn't a Combi ( my assumption sorry ) and that makes it a bit more relative to your application. A quick browse sees average MCS installs at between £5k to £6.5k. 

A regular system boiler would be circa a grand, so about £1800 fitted ( retro fit price ). That leaves you the £2.5k you need for your genny, plus between £700 to £2.2k to run it. 

Dont forget that the CHP baxi only produces 1kw when delivering the full 6k of the primary gas burning side . Best to yank all your insulation out and drill a few vents in here and there to increase your gas usage . ( been a long day, sorry ). 

With a low energy house you may struggle to get any meaningful electrical generation tbh, and I was reading about this from 06:00 to 09:00 this morning so have researched as much as I could before replying ( still not long enough to realise it wasn't a Combi though. D'oh!  ). 

With the stand alone genny you'll be able to produce heat and or electricity when you need it most, rather than have the boiler dictate when you get additional electricity. 

What is your design heat loss in kW? 

 

[readiescards]

So the Baxi Ecogen (in its current design) is not looking the way to go, thanks for your time and effort in researching it :-)

 

According to @JSHarris Fabric and ventilation heat loss calculation is around 3kW in winter (note I've upped the ACH to 3.5 as got less confidence in the house air-tightness now its built - still to be measured)

[readiescards]

Still no news to report on the Baxi Ecogen replacement model - will update this thread if I find something out

[Nickfromwales]