Wood boiler for greenhouse

[chatelot16]

the buffer tank is not used to reduce the temperature but to store heat, for regular heating of the house, with an intermittent operation boiler

for a little extra heat in a greenhouse the regularity is not very important ... I, do not see the usefulness of the buffer tank

if it is necessary to limit the temperature of the hot water, the classic solution is the thermostatic 3-way valve ... even if the boiler is at almost 100 ° C it sends water at 35 ° C in a heated floor if it is is set at 35 ° C

the temperature limitation by 3-way valve allows the use of polyethylene pipes for heating!

to discuss more it is necessary to speak about greenhouse surface to heat, and temperature: a greenhouse is not very insulated: it is thus practically possible only a small increase in temperature: no need for thermostat, one is satisfied to balance a certain power, and it's been a few degrees more than if we did nothing

[dedeleco]

The buffer tank is used to heat by loading wood which burns quickly but if no plant is in the ground, then the earth makes a very good buffer (like the concrete of a house) if the exchange surface is sufficient and therefore the buffer tank is unnecessary, just a three-way channel ensuring a more constant temperature of the boiler and the floor.

[Did67]

Yes very useful in case of problem ...: cheesy: but in "normal" use (99.9% of the time) it does not have to "spit" ...

But yes you have to mount one, otherwise there are material risks, even human ...

Let's be clear: like any security device, it is there to never operate in normal operation, but to avoid an accident (boiler explosion) in abnormal operation (the boiler heats up but the circulator stops, for example! As we are "flat", no thermosyphon, so it ends up in a steam locomotive by farting at the most fragile point!).

So, yes, absolutely put one!

[chatelot16]

the safety valve is essential when the expansion vessel is a pressurized tank ... but do not forget the simplest solution: expansion vessel open in height! if it boils, it just makes this vase overflow ... I know who we have old wood-fired boilers, who voluntarily put the overflow of the expansion tank in front of the kitchen window: when it overheats we see the water fall

the problem with this kind of tall vase is to protect it from freezing ...

[Did67]

Indeed, we can treat the question like that too ...

[antoine35]

So there you have it, I have some additional info about the system.
the boiler is a unical from 1988 with a power given for wood of 40kw.
the greenhouse has a volume of less than 800m3.
the floor is made of high pressure pvc for the nurses and "plymouth? (flexible)" between them.

so I have other questions ......

While browsing the site I found various connection diagrams and I am therefore thinking of putting a buffer tank of several thousand liters that my colleague will tinker with a recovery tank, like water or fuel tank .......


1 / what to do with the DHW outputs on the boiler? I thought I would do nothing at all by leaving them open: good or not?


outlet of the buffer tank, put an automated three-way for the regulation of the water flow (he thinks that 40/45 ° will be the maximum for the plants)

2 / the outputs of the boiler are in 40/49 and I thought to go out in 28copper to feed the balloon and ditto at the output of this one towards the nurseries of the "heated floor"

3 / I have grundfoss 20-50 and 25-60 circulators but I don't know if they will be enough.

4 / I also saw somewhere that in addition to the thermal valve, a safety thermostat could or must be installed


5 / what type of expansion tank should I install?

voili, voilou for the details ... thank you to you
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[dedeleco]

The safety thermostat cuts off the heating when the maximum water temperature is reached, 95 to 100 ° C, easy by cutting off the gas or oil supply (mandatory then), but difficult to remove the wood for a boiler with drink !!
Unless you put an alarm signal, if too hot for lack of water and stop the boiler.
Does the boiler have a combustion fan?
http://doc.unical.fr/notices_techniques ... _05_06.pdf
http://doc.unical.fr/doc_commerciales/U ... OKOLUS.pdf
In this case the thermostat stops combustion by stopping this fan.

So it is better to be sure not to put too much wood to burn compared to what the boiler can evacuate in heat, especially as the boiler is powerful. Otherwise fire with the boiler melting (reason for the safety valve not to have an extra bomb)? !!
It all depends on the weight of the boiler to absorb excess heat;

The DHW is part of the boiler exchangers and you must see their arrangement and relative surface and the boiler manual, but a priori it is better to have water circulating in it which risks being well heated.

The expansion vessel has a volume greater than the expansion volume of the circulating water, therefore function of the volume of circulating water and its temperature therefore calculation to be made with info on econology !!
The type is less crucial, membrane near the boiler often short-lived (quickly porous membrane) and therefore an old-fashioned vessel at the top of the installation is also practical, in my personal opinion not to change the vase every 5 years.

If no plant is found with the roots in the earth, the thermal buffer can simply be the soil of the greenhouse with exchanger pipes 30 to 50cm deep in sufficient length, for an effective volume much greater than that of a balloon. . A small balloon may then suffice.
For the boiler to be well cooled, it is better to respect the boiler outlet diameters, i.e. 40/49 so that enough water circulates in the boiler to cool it well (otherwise too much pressure drop which increases as the reverse the diameter to the power 4 to 5 is if we divide the useful diameter by 2, the pressure drop is multiplied by 25 !!!), even if it means multiplying the circuits in parallel to use pipes of smaller diameter.
It is good to have the boiler manual
which on unical:
http://www.unical.fr/chaudieres-bois-granules.php
, the flow rate to be respected, to calculate the pressure losses for the lengths and diameter of pipes (see charts on econology that I had used for Okofen and Pellaqua, insufficient heating problem https://www.econologie.com/forums/post185617.html#185617
) and choose the right circulators.
The surface of the greenhouse and how much for 800m3, 400m2 approximately for a height of 2m?
The insulation is how much, in which region or which sun, for a poorly insulated house, from 300 to 400m2, 40 Kw seems a little weak, for a greenhouse everything depends on the desired temperature with which outside temperature (in the middle of winter with -15 ° C for tomatoes at my fingertips, 40Kw is insufficient or only in spring or early autumn we do not need the same powers)
In conclusion, it is better to assess the necessary orders of magnitude with sufficient precision.
For a greenhouse, it is good to make the best use of solar heating.

[antoine35]

yes it is equipped with a fan so I will couple it with a safety thermostat in this case.
for the ECS I circulate it on the buffer ???

the exchangers are barely covered with earth so no buffer !!! putting the earth back is not too possible ....

the surface is about 300m2 in ille et vilaine and it is only insulated with a double tarpaulin roof and the walls are those of a classic greenhouse so a simple tarpaulin.

my colleague also thinks that 40 kw will be fair but currently it runs on gas and the prices rise quickly, on the other hand it has wood in quantity

I found the unical TS 2 doc but no information on the flow it should receive .....

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[manitou22]

Hello,
I have a unical wood that I bought last year for 100 euros; it is at least ten years old, it is the lada of reverse combustion wood boilers: no electronics, the adjustment of the high and low operating temperatures of the fan is manually adjusted by against a very average efficiency because of an adjustment very imprecise primary and secondary air (tubes that are screwed more or less at the end of the ventilation openings - almost all or nothing), poorly designed internal air ducts (the wood in the back burns twice slower than the one near the door), an opening to the combustion chamber that is too large so that the gasification is only intermittent; in short, it is a rather capricious machine to pilot.
I had coupled it to a thousand liter balloon that disconnected it and I connected it live so that it works despite being oversized in relation to my floor area. The blower cut-out at maximum temperature replaces the tank.
For a greenhouse installation, I would couple it directly to unit heaters to start, so as to see if its capacity is sufficient before embarking on a more complex installation.
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[dedeleco]

Listen to the experience of manitou22, but it would be good to specify your installation more:
Your 300m2 greenhouse is already working with barely buried exchangers of what surface with what arrangement, with what volume of soil on it which, even a few in appearance, quickly produce m3, as an exchanger with a total surface area of ​​10m2 at a depth of 10cm makes more than 2m3 of earth (above and below), a beautiful buffer already!
What is the power of the gas boiler?

So you can follow manitou22 and connect directly in parallel with the gas boiler (with valves of choice), with safety valve, fan cut off if more than 90 ° C for the water (take an adjustable thermostat in T) and control the quantity of wood which burns to fix the power (40KW corresponds to 8 to 10kilos per hour of very dry wood which burns at 100% of output).

Additional solar collectors in winter would be useful.

To monitor yield, you need to measure the temperature of the flue gases leaving and adjust the power to prevent it from exceeding 130 ° C to 150 ° C, also valid for the gas boiler, which makes it possible to avoid sending a large proportion of the heat in pure loss outside !!