Advice on (very) low output oil condensing boiler

Eoghan Barra

Hi folks,

Am currently building a house that will be insulated to passive standards, should have high level of airtightness, will have hrv and so on. Will be using a room-sealed dedicated wood burning stove as principle form of space heating for entire house.

I'm looking at installing an oil-fired condensing boiler for dhw (we don't use much) and to heat one small rad in each of the 2 bathrooms. However, I have been told by local heating contractor that they don't really come with an output of less than about 17kW, which he can somehow tweak down to about 15kW. He said this would be quite inefficient for such a small requirement - that a boiler with an output of about half that would be much more efficient in this situation but that they aren't available with such low outputs.

I'm not that that clued-in on these matters, but that's the jist of it.

Can anyone advise on how this issue might be overcome, or know of any low output oil-fired condensing boilers, say about 8kW?

Any thoughts gratefully received.

heinbloed

Your architect/planner should have thought about that.

ThermMix, WeisshauptWTC15, Boesch ThermoCondensWTC-OW to name a few.
All modulating from about 5-15kW.

Honestly: it is cheaper to heat a PH with direct resistance electricity than with two or three independant thermal sources. All thermal installations demand high running times, the less each of them is used the longer the amortisation will take.
Anual maintenance of boilers and burners and chimney (sweeping) costs as in your project will make a PH thermal supply as proposed very,very energy intensive.

heinbloed

Here a log-boiler for dual fuel use:

http://www.ligno.at/htm_A/HolzmaxF_b.html

Logs + gas
or
Logs + (vegetable/mineral)oil
or
Logs + pellets (from december 2012)

Output 15-20 kW, can be down-modulated to 50% =7.5-10kW. Lambda probe !

But first check the actual thermal demand, 7.5kW for a single family PH seems to be way-out.

Eoghan Barra

Hi Heinbloed,

Thanks v. much for your interesting reply.

The wood burning stove is definitely going in as we have a free source of fuel from our land; we also love the feel a wood stove gives to a home. It's really just how to heat the 2 small rads and dhw that I'm unsure about.

The seai gives the delivered energy cost of electricity as 52.94 cents/kWh, as opposed to 9.1 for oil, i.e. almost 6X more:

http://www.seai.ie/Publications/Statistics_Publications/Fuel_Cost_Comparison/Domestic_Fuel_Costs_Comparison_April_2012_pdf.pdf

But if I understand correctly, you are saying that because the energy requirements are so low in this situation electricity will work out cheaper when you factor in the maintenance costs for an oil-based system?

Do you really think electric showers, immersion for other dhw and electric rads (I presume that's the alternative you're proposing) would have lower running costs than oil, all things considered?


I've just seen your second reply now. We're really decided on a wood burning stove that will add atmosphere to, as well as heat, the house (probably a Saey Gustav), so the Holzmax wouldn't work for us. Thanks anyway.

heinbloed

Electricity costs around 20 cents per kWh (household tarif in the Rep. of Ireland). Self-produced PV is already cheaper, even with the most expensive DIY PV installations.

http://www.minijoule.com/en/newsletter/archive/view/id/155

http://www.youtube.com/watch?v=k3jkDFSDPrU

There are many other (cheaper) electricity sources.



Get the thermal energy demand calculated and then you can compare like for like.
The EN standard for this demand calculation is EN12831.
Ask your architect/planner to get this done.

Maintenance and replacement costs plus running costs (fuel and auxillary energy) must be part of the calculation. Without these you will be lead into an salesman trap.

Whoever sells a heating system for your structure (architect, engineer, installer etc.) should be asked for the guaranteed price per used kWh. To get straight answers ask straight questions.

Eoghan Barra

Thanks again Heinbloed for another very useful reply.

That's an interesting system there, the minijoule. Do you have any idea how much electricity each panel provides? Do you have any experience of these yourself?

nuzzer

give him a few days to google it first and maybe surgically remove his dictionary from his anus and he will come back with some form of dribble

Billy Bunting

nuzzer wrote: »

give him a few days to google it first and maybe surgically remove his dictionary from his anus and he will come back with some form of dribble

You need to chill nuzzer, heinblower will grow on you.

bryaner

nuzzer wrote: »

give him a few days to google it first and maybe surgically remove his dictionary from his anus and he will come back with some form of dribble

Very helpful post..:rolleyes:

heinbloed

Eoghan Barra asks:

That's an interesting system there, the minijoule. Do you have any idea how much electricity each panel provides? Do you have any experience of these yourself?

No, but you can figure this out yourself using PVGIS. Location and positioning are important.
As said there are cheaper PV systems for plug and play solutions. They had been brought to the shop front via the USA about 1-2 years back, the inverter being part of the panel.
Others are following, the idea is simple enough. It saves the midle-men and the paper hustle with selling and metering.

Check for the guaranteed output over a long time, 10-20 years to compare the systems.
GP Joule has a long record in the large scale PV sector so my first look would be with them. And you get a small house with each panel for free:)

Again: check with your planner for the actual energy demand before deciding on any heating system.


PS
Here a link to an older thread about small, oil-fueled modulating condensing boilers with some usefull links:

http://www.boards.ie/vbulletin/showthread.php?t=2056449851

Eoghan Barra

Heinbloed, I'm very grateful for all of your advice.

I think you may have single-handedly helped crack a problem that has been driving me mad for months. I was never comfortable about installing an oil-fired boiler (I'm not crazy about fossil fuels) but didn't see any cost-effective reliable alternative. What you have written makes perfect sense, however, and my feeling now is that I will be going electric with something along the lines of a couple of minijoules as you suggest. (The wood-burning stove will still provide most of the space heating obviously.)

It appears that the minijoules are plugged into a socket in the house, thereby providing (some) electricity. Can they also be connected directly to your electricity circuit permanently, ie not via a socket?

In my situation, the only directly south facing roof (I would want them on a roof) with space for these would be on an outhouse about 25m from the main house, which will share the same electricity supply. Do you see any problem with connecting the minijoules there?

KoolKid

2nd and final warning for nuzzer. Another post like that gets you a weeks holidays.

heinbloed

It appears that the minijoules are plugged into a socket in the house, thereby providing (some) electricity. Can they also be connected directly to your electricity circuit permanently, ie not via a socket?

In my situation, the only directly south facing roof (I would want them on a roof) with space for these would be on an outhouse about 25m from the main house, which will share the same electricity supply. Do you see any problem with connecting the minijoules there?

All electricity generators must be separable from the grid, a technical rule. All generators must have an automatic emergency cut-off to avoid electrocution of electrians working on the grid during main power failures.

Read the Irish regulations!

Grid seperators and meters can be purchased via this company as well (EN conform equipment).

These types of PV panels make economical sense when there is a permanent day-time baseload to be covered. For example caused by CH circulation pumps, cooling and ventilation, heat pumps etc.. wherever the permanent base load (the permanent minimum draw from the public grid) is partly or totally covered.

Simply because less units (kWh) are charged by the public electricity provider. The ESB meter runs slower, so to speak.

For a PH with a permanent base load(ventilation and heating) an ideal solution: the expensive day-time load reduced.
Intelligent meters are not far away, we must calculate with our low PV/grid penetration in Ireland with increased day-time(peak load) tarifs.

These simple Mini PV installations do not generate a monetarian income, electricity generation won't be counted and sold to the grid. Any surplus generated will not be metered or sold, turned into money.
This could be done technically, the additional equipment is available as said before.
But there are cheaper (€/kWh) and larger (m2) installations for this selling purpose.

As long as the Mini PV installation is installed after the official meter it works. The electricity generated and used at the same time won't be metered by the ESB.
The miniJoule home page offers some calculation samples for Germany, like €55.- saved per year and panel, €110 per two panels etc..
But this realy depends on your actual electricity costs for the purchased electricity (grid)and the harvest (positioning).

What makes these small plug-and-play installations economical is their simplicity. Everyone can install and use them.

Unless one has the brain of a mercenary, this would need some special training to handle plug and socket:

http://www.huffingtonpost.com/2012/03/23/us-army-solar-generator-training_n_1375687.html


http://energy.gov/articles/energy-department-announces-funding-develop-plug-and-play-solar-energy-systems-homeowners

There are oceans between us (smiley).

shane0007

Well done Heinbloed, a very well informed and helpful post. You have certainly earned well above my respect on this one.

Eoghan Barra

Yes, mine too. Fair play to you Heinbloed.

heinbloed

I found this article reporting about the price for home-made electricity, refering to Bloomberg:

http://www.renewablesinternational.net/bloomberg-says-solar-is-here/150/510/38375/

So it might make sense to save the chimney and the boiler plus tank/metering costs, fuel and maintenance/replacement costs etc. and go for direct electric (water storage) heating.

cheviot26

Hi
Would you mind sending me the details of the wood burning stove you used (pm)
I am building a house similar to yours and am finding it very hard to source a suitable stove