Heating system retrofit/redesign

mickleod

Hi everyone,
Was just having a look around and trying to decipher what the best home heating upgrade for my needs is.

Have done a bit of research and feel that this is what I have;

110m2 house, semi-d dormer bungalow, two people living in house, with a few more planned...!

Early 90's construction, recently insulated to best level achievable (50mm sprayfoam insulation behind new plasterboard on external walls, 400mm glasswool attic insulation).

Copper dhw cylinder, badly fitted into narrow hotpress with a lagging jacket just thrown over it. Since we bought house 2 years ago, we haven't once used hot water thru the taps. We could live without it, but would obviously like it. Electric showers made this possible, kettle boiled for wash up etc.

OFCH installed on heating diesel, outside boiler is there since house was built, so ~20 years old (ie due for replacement). Oil pump is definitely on the way out, given by the noise it makes, but still ticking away for the moment.

4kW solid fuel stove in sitting room, self-install, heats seating area nicely. I have a good source of cheap timber so solid fuel is way I want to go for the future. With that in mind I have a 16kW (5kW to space, 11kW to boiler) stove sitting in the kitchen/living area waiting for install. Very compact house, good heat circulation thru space so opening a door from kitchen will do a lot for ground floor heating when this is installed.

My question is how to set the system up to be as future proof as possible. My intention is to install solar in future, and replacing oil boiler with a woodchip when the funds allow (though if we are able to fill our needs thru solar and solid fuel, a ~20kW oil-fired high eff boiler might be a reasonable alternative, given the capital cost of wood-pellet boilers and the storage requirements).

This is what I'm thinking;

200 or at a push 300 litre thermal store, 3 input coils (solar, stove boiler and main boiler circuits), mains pressure dhw output coil, heating circuit output coil.
similar to: http://www.chelmerheating.co.uk/ecocat_thermal_store.htm

Upstairs heating to be supplied from stove boiler once thermal store achieves temperature (3 port valve with thermostat in thermal store, or heating circuit thru thermal store kicks in?)

Laddomat 11-30 charger to be plumbed into stove boiler circuit, to achieve best efficiency for system (http://www.termoventiler.eu/media/upload/LM11-30_Manual_Med%20LMpump_E.pdf)

My main aim would be to use the external boiler to back-up the stove boiler (winter) and solar system (summer), and in a "switch-on" capacity, ie. when you get back late on a Sunday evening and just want to heat the house up a bit without the bother of lighting the stove.

Plumbing is pretty accessible due to side-attics, so retro-fit shouldn't be too difficult.

My questions about this are;

- how do I account for expansion in the boiler stove system using the thermal store setup; via venting the stove boiler circuit? expansion vessel?

- how do I make the boiler stove system safe in case of electrical power outage and pump outage (there is a thermostatic air supply cutoff (closes the secondary air supply to the stove) on the stove but this is dependent on the primary air supply being shutoff which I would not like to fully depend on). Could you have a valve which on power outage opens and allows the Laddomat to be bypassed and allows gravity flow? A bit complicated perhaps.... I'd like to think that someone would generally be in the house when the stove is firing but you'd need redundancy I'm sure.

- I've seen suggestions that a combination of a thermal store and a seperate domestic hot water cylinder would be viable, though I think that my system would be a bit small to warrant it. I'm probably going to need to make hot press area a bit bigger to accommodate new thermal store, but I also have an insulated side attic which I can use. I like the idea of mains pressure hot water as well though...

-my reading of the Laddomat device suggests that it would be useful for a few reasons;

increased lifetime of the stove boiler, due to decreased corrosion (ie less condensation/tarring of the external surface of the boiler in the firebox)

better efficiency within the firebox as higher temperature achieved there

less tarring of flue due to higher temperature burning

better performance of thermal store, as less mixing (cold supply to stove boiler taken from bottom of store, hot feed to top of store)

are these reasonable assumptions and does it justify the extra 200 quid outlay?

There is a lot of info on this forum, but it's hard to tie everything together for your own individual requirement. Hopefully someone will have an opinion/advice or previous experience of a similar install, and I appreciate your feedback in advance.

Thanks,
Mick.

JohnnieK

mickleod wrote: »

My questions about this are;

- how do I account for expansion in the boiler stove system using the thermal store setup; via venting the stove boiler circuit? expansion vessel?

- how do I make the boiler stove system safe in case of electrical power outage and pump outage (there is a thermostatic air supply cutoff (closes the secondary air supply to the stove) on the stove but this is dependent on the primary air supply being shutoff which I would not like to fully depend on). Could you have a valve which on power outage opens and allows the Laddomat to be bypassed and allows gravity flow? A bit complicated perhaps.... I'd like to think that someone would generally be in the house when the stove is firing but you'd need redundancy I'm sure.

- I've seen suggestions that a combination of a thermal store and a seperate domestic hot water cylinder would be viable, though I think that my system would be a bit small to warrant it. I'm probably going to need to make hot press area a bit bigger to accommodate new thermal store, but I also have an insulated side attic which I can use. I like the idea of mains pressure hot water as well though...

1. An open expansion pipe continuously rising to a feed & expansion tank in the loft will solve this problem. the solid fuel stove must not be sealed.

2. again a continually rising open expansion pipe would work if there is a power outage. It must be unrestricted from the stove to the feed & expansion tank.
You will need a thermal store of at least 500L to work correctly so you will be increasing the foot print of the hot press considerably when you factor in pipe work and also maintenance later on. I have only heard this week about conecting a hot water cylinder to a thermal store so I have not knowlage of the benefits of this.

shane0007

With a 110m2 house, you will require a lot more than 11kw to the heating. 300L cylinder will take 6kw. Each 1000 x 500 radiator single will be 1kw and 2kw for a double. Add 10% for pipework losses.

The efficiency of the solid fuel will be in the region of 40% so your 11kw now becomes 4.4kw!