What’s the alternative

[recoveringbuilder]

Coming into the second winter in the house and still not happy with the heating system. Recently had to have a new motherboard fitted on the biomass as well as a new display, the casing on the motherboard had melted! The problems we are finding are; when there is no call for heat all is well and the tank gets up to its temperature no problem but when we get a call for heat to the ufh and the radiators upstairs it very quickly loses temperature and goes down to around 29 degrees both top and bottom of the thermal store, at this point the ufh is still calling for heat and if we leave it to do that it will take somewhere in the region of 5 hours burning to satisfy all the needs and get the ts back up to temperature. When we had the chap here doing the repairs on the biomass ( he wasn’t the installer but someone that they sent out as he was closer to us) we told him we weren’t exactly happy with the system and that we were thinking about installing an oil boiler in the garage to work alongside the biomass. He agreed this could be done and  explained how it would be done and said he would be happy to help with the connection but we are now wondering if the thermal store is the problem and that we might be better with a megaflo. We really need to get this sorted out once and for all as we don’t know from one day to the next how it’s going to perform, some days the house is lovely and warm , everything up to temperature then the next day it seems to be struggling to supply everything needed. Any thoughts?

[SteamyTea]

How large is you thermal store, your objectional biomass burner, and what are you heat loads?

[recoveringbuilder]

Thermal store is 500l , boiler is 18kw klover inset , as for the heat loads we don’t know as this was left to the installer to work out.just looked at the EPC and it’s saying 15,900kwh for heat and 2500kwh for hot water does this help?

Edited December 15, 2020 by recoveringbuilder
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[Declan52]

What are your set programs l? Does it come on and off when you want it to??

What way are you using the ufh and rads call for heat???

If nothing is calling for heat how long does it take to get to your set point in the thermal store??

500l is a massive tank of water to heat.

[PeterW]

Biomass boilers generally can’t work without a store or buffer so you would need to keep something for the pellet stove to dump into. 
 

Sounds like the store is piped wrong - ideally it should take water from the bottom 25% for heating and the top 50% for DHW - have you got

a schematic of the tank showing the connections ..?

 

Assuming that the tank is at 35°C and you want it to 72°C, and flat out the pellet boiler is giving 6kW direct to the heating and the rest to the TS, it should be fully loaded inside 2 hours. Sounds like something is out of whack on the pellet boiler - how many pellets is it using per burn or per day ..?

[recoveringbuilder]

We don’t have set programs, it comes on and off as it needs to. The room stats are set at 19 degrees in the living areas, lower in the downstairs bedrooms and the radiators at present are only put on for a couple of hours at night . If nothing calls for heat the boiler fires up when the top of the ts drops to 60 degrees and doesn’t take too long ( maybe an hour) to heat up to temperature again. I have noticed however that there is quite a delay from when the tank hits 60 , burner starts up but by the time the flames are going well the tank can have dropped a further few degrees.

[SteamyTea]

I shall, for the matters of implicitly, reduce that heat load to 12,000 kWh/year, and assume that the heating is on for 160 days.

So that is a mean of 75 kWh/day.

But on the coldest days, you will need at least twice that, 150 kWh.

 

Now your boiler is 18 kW, at its very best, in ideal circumstances, but probably closer to 15 kW.

So it needs to run, just to cover the heating loads, between 5 and 10 hours a day.

 

Edited December 15, 2020 by SteamyTea

[Declan52]

How hot are you storing the water in the tank??

[recoveringbuilder]

2 minutes ago, SteamyTea said:

I shall, for the matters of implicitly, reduce that heat load 10 12,000 kWh, and assume that the heating is on for 190 days.

So that is a mean of 75 kWh/day.

But on the coldest days, you will need at least twice that, 150 kWh.

 

Now your boiler is 18 kW, at its very best, in ideal circumstances, but probably closer to 15 kW.

So it needs to run, just to cover the heating loads, between 5 and 10 hours a day.

 

Are you saying in your opinion that the boiler is not big enough ( which is something that we have suspected for some time)

[recoveringbuilder]

2 minutes ago, Declan52 said:

How hot are you storing the water in the tank??

70 degrees 

[SteamyTea]

1 minute ago, recoveringbuilder said:

Are you saying in your opinion that the boiler is not big enough ( which is something that we have suspected for some time)

Well short of something being wrong with it, and the EPC numbers being well out, I would think it is.

[recoveringbuilder]

8 minutes ago, PeterW said:

Biomass boilers generally can’t work without a store or buffer so you would need to keep something for the pellet stove to dump into. 
 

Sounds like the store is piped wrong - ideally it should take water from the bottom 25% for heating and the top 50% for DHW - have you got

a schematic of the tank showing the connections ..?

 

Assuming that the tank is at 35°C and you want it to 72°C, and flat out the pellet boiler is giving 6kW direct to the heating and the rest to the TS, it should be fully loaded inside 2 hours. Sounds like something is out of whack on the pellet boiler - how many pellets is it using per burn or per day ..?

We are using around 30kg of pellets per day

[SteamyTea]

30 kg is about 135 kWh primary energy.

So once efficiencies are taken into account, you may be getting 100 kWh into the thermal store.

[PeterW]

1 minute ago, recoveringbuilder said:

We are using around 30kg of pellets per day

So you are getting approx 145kWh from that - that is a lot of heat ..!! Is that all the time or just when it’s cold .?

[recoveringbuilder]

3 minutes ago, SteamyTea said:

Well short of something being wrong with it, and the EPC numbers being well out, I would think it is.

So what size would you think it should have been 

[SteamyTea]

Hard to say, as generally, biomass burners need to work at their maximum to be most efficient.

 

It could be that the heat losses from the TS are higher.  Where is it situated? How well insulated is it?

 

Taking @PeterWfigures, the store holds about 18 kWh of useful thermal energy.  So should heat up in 2 hours.

[recoveringbuilder]

1 minute ago, PeterW said:

So you are getting approx 145kWh from that - that is a lot of heat ..!! Is that all the time or just when it’s cold .?

I wouldn’t mind if it was a lot of heat however it isn’t presenting itself as such! Bedrooms are never above 17 degrees, if we set them any higher it would burn continuously , we haven’t had any real cold weather as yet so consumption will only get higher!

[Declan52]

Why have they set the boiler to come on when it's only dropped 10 degrees. I found my sweet spot for storing hot water and using the boiler it's most efficient was 64 degrees. 

How much insulation is around the tank??

If nothing is used how long does it take to drop 10 degrees before the boiler would fire up??

Are all your pipes entering/leaving the tank insulated??

So on an average coldish day what way do you run it. Something like this.

Boiler gets turned on in the morning and ufh calls for heat plus the rad gets a blast. This takes X hrs before the ufh stops needing heat. Then it burns for X hrs to reheat the tank. 

[recoveringbuilder]

9 minutes ago, SteamyTea said:

Hard to say, as generally, biomass burners need to work at their maximum to be most efficient.

 

It could be that the heat losses from the TS are higher.  Where is it situated? How well insulated is it?

 

Taking @PeterWfigures, the store holds about 18 kWh of useful thermal energy.  So should heat up in 2 hours.

It’s in a little room off the utility room , bio Quattro tank , all pipe work insulated with foam pipe insulation,  felt lagging and topped with foil faced bubble wrap 

[recoveringbuilder]

10 minutes ago, Declan52 said:

Why have they set the boiler to come on when it's only dropped 10 degrees. I found my sweet spot for storing hot water and using the boiler it's most efficient was 64 degrees. 

How much insulation is around the tank??

If nothing is used how long does it take to drop 10 degrees before the boiler would fire up??

Are all your pipes entering/leaving the tank insulated??

So on an average choldish day what way do you run it. Something like this.

Boiler gets turned on in the morning and ufh calls for heat plus the rad gets a blast. This takes X hrs before the ufh stops needing heat. Then it burns for X hrs to reheat the tank. 

It is controlled with an lk controller and the program relating to our set up brings it on after the 10 degree drop.if nothing is on it can stay off most of the day( as it did yesterday ) everything is well insulated. 
boiler just comes on and off itself so it will come on during the night when obviously the outside temperature has dropped and the house is cooling down. This is only for the ufh , radiators only get a couple of hours in the evening. I honestly wouldn’t like to try to heat upstairs continuously as it definitely wouldn’t cope with that.

[Declan52]

How big are the rooms upstairs and how big are the rads. It shouldn't take hours to heat any room and yours isn't even what you would class as warm.

[recoveringbuilder]

15 minutes ago, Declan52 said:

How big are the rooms upstairs and how big are the rads. It shouldn't take hours to heat any room and yours isn't even what you would class as warm.

6x4 rooms, radiators 1200x600 or 7.5 btu

[recoveringbuilder]

 have you got

a schematic of the tank showing the connections ..

 I will have a look for this in the morning @PeterW

[Temp]

If I've understood correctly it heats the store from say 60 to 70C in about an hour with no heating load.

 

Power = Energy/Time = (4200 * 500 * 10) / (60 * 60) = 5.8KW

 

I think I would be inclined to do an experiment and let the store go cold (say 30C). Then with nothing calling for heat fire up the boiler and measure more accurately how fast it heats up and redo the sums as it sounds like its down on rated power. 

 

 

 

 

 

 

[recoveringbuilder]

So today has been really cold, a freezing fog that hasn’t lifted all day.Really struggling to get the heat up in the house, have spent most of the day tank watching, it heats up to its temperature but as soon as a couple of zones call for heat within half an hour the  tank is down to about 29 degrees top and bottom, at this point there’s no point in leaving the ufh on as the water isn’t hot enough to heat it and I know the fire will burn all day but never getting the tank up to temperature.

 I have looked at the epc and it says heat loss is 18.15kw . I have also looked at the spec of the burner and found that despite the installer telling us it was 18kw it is in fact 14.7kw with 2.2 going to the room and 12.5 to the thermal store. Something is not adding up here, I sent the installer an email between Xmas and new year telling him we were still having problems, I knew he was not working at this point but wanted to register the complaint as quickly as possible before our warranty runs out this month, of course he hasn’t answered! I have tonight sent an email to firepower heating who are the distributor in this country and told them about all the trouble we are having and I’ve also said I suspect the installer has made a mistake on the spec and that we should have had the larger stove. I will see what response I get from them , I don’t know what else to do but was wondering if the energy savings trust would have anything to say about this since the installer is on their mcs list and also that we got the interest free loan from them for installation. Or do I get an independent engineer to have a look and end up going to a lawyer with it, I just feel I am going to be paying back this loan long after the appliance is binned!

Edited January 6, 2021 by recoveringbuilder
Correction