Green Building Bible, Fourth Edition |
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Posted By: Peter_in_HungaryThe TS, at 400lts won't act as a conventional TS as usually discussed here i.e. a heat store to provide when the wood burner is out, but it should be enough to act as a buffer to stop the boiler short cycling. I would expect that the boiler would short cycle much more if the TS was removed, especially when it is lightly loaded. IMO it should be plumbed in so that the boiler heats the TS and the CH and DHW run off the TS - is that how it is plumbed? (along with the usual 3 way valves to control the CH return/flow temps) DHW must be indirect somewhere - how is that managed? Inhibitor should not be a big expense, once it has been put in, how often are you changing the water or topping up the inhibitor? Air/gas usually collects in a 'favourite' place in a system - and that's where you put the air bleed valve (AAV) Is the air a new problem and did anything change to cause this.
Posted By: ringiHow is the boiler burner controlled?
Is there a thermostat at the top of the TS to turn off the boiler and at the bottom to turn it on?
If the boiler is controlled on its own internal thermostat, can you set the T it is turn on at to be higher then the T it is turn off at?
I assume you have a pump from the boiler into the top of the TS, then the bottom of the store connected to the boiler's return, with a separate pump from the top of the TS to your heating, return into the bottom of the thermal store.
I am expecting that your TS is not plumbed correctly or there is a control issue as 400lts should be more then enough to act as a buffer to stop short cycling.
Posted By: GotanewlifeI had no problem power flushing my system I just connected it up either side of the TS so it didn't go through the TS. As PiH says 400 litres is plenty for a buffer but nowhere near enough for a TS, and without it I would have thought you will get loads of short cycling
Posted By: JonGAlas the UK hasnt followed NE design.
Posted By: JonGIn terms of your gas issue, if it is combustible it may very well be a byproduct of corrosion in the system somewhere, but overdosing with inhibitor is not necessarily the answer.
Have a look at the German regs VDI, which provided fill water is soft enough and ph values can be achieved no inhibitor is required and in general terms can actually be detrimental.
It's tough with an OV system, but plates can minimise the amount that is OV.
Posted By: JonGNE is Northern European who have far more experience of using biomass than we do.
Plates are plate heat exchangers which can be used between open vent and sealed systems, so that as much as possible can be kept sealed and better protected from corrosion.
Posted By: Peter_in_HungaryThe TS, at 400lts won't act as a conventional TS as usually discussed here i.e. a heat store to provide when the wood burner is out, but it should be enough to act as a buffer to stop the boiler short cycling. I would expect that the boiler would short cycle much more if the TS was removed, especially when it is lightly loaded. IMO it should be plumbed in so that the boiler heats the TS and the CH and DHW run off the TS - is that how it is plumbed? (along with the usual 3 way valves to control the CH return/flow temps) DHW must be indirect somewhere - how is that managed? Inhibitor should not be a big expense, once it has been put in, how often are you changing the water or topping up the inhibitor? Air/gas usually collects in a 'favourite' place in a system - and that's where you put the air bleed valve (AAV) Is the air a new problem and did anything change to cause this.
Posted By: Jeff BBut now you've got me thinking again! My thermal store has an unused coil in it. This could be used to circulate the boiler flow (instead of direct heating as it is now) and the two tappings currently used for the boiler flow and return could be used to couple up to a PHE to feed the C/H system. Would that work do you think? That way the thermal store would simply be a reservoir of hot water and I could pressurise the whole system, getting rid of the F&E set up altogether?
Posted By: Jeff BThe boiler flow is directed to both the DHW cylinder and the TS; when the DHW cylinder is satisfied, a motorised valve closes the boiler flow to that and it carries on to the TS alone until that in turn is satisfied.
Posted By: Peter_in_HungaryPosted By: Jeff BBut now you've got me thinking again! My thermal store has an unused coil in it. This could be used to circulate the boiler flow (instead of direct heating as it is now) and the two tappings currently used for the boiler flow and return could be used to couple up to a PHE to feed the C/H system. Would that work do you think? That way the thermal store would simply be a reservoir of hot water and I could pressurise the whole system, getting rid of the F&E set up altogether?
It is generally not a good idea to use an indirect coil to put heat from a boiler to a TS - there is just not enough capacity of heat transfer to cope with the output of the boiler and serious short cycling or over heating of the boiler would be the likely result. Before you further contemplate this move check the rating of the coil and match this to the output of the boiler to see how they match.Posted By: Jeff BThe boiler flow is directed to both the DHW cylinder and the TS; when the DHW cylinder is satisfied, a motorised valve closes the boiler flow to that and it carries on to the TS alone until that in turn is satisfied.
Sounds good - I presume the indirect coil could not handle the full output of the boiler so a parallel feed is needed. Does the boiler short cycle lots if the heating is not on (i.e. temp satisfied in the TS) but the boiler is used for DHW
BTW I am not a fan of plate heat exchangers when used with a TS as the PHX needs a high flow rate to get the rated heat output and has return temps. both of which conspire to wreck the stratification that is so important to get usability and efficiency out of the TS
Posted By: ArtiglioThe plate exchangers in my system were bought off of ebay using little more than educated guess work, tgether they were under £150, the pumps on the domestic heating side are normal central heating pumps (reused those in the old lpg systems)
There is a problem of the boiler sometimes being fired up when the buffer receives a slug of cold water from the 25m unfderground pipe running from boiler shed to house.This now rarely happens after altering demand timings and boiler settings But statification in the buffer is not as crucial as it would be in a thermal store.
The use of plate exchangers has meant the old heating circuits have no way of contaminating the new boiler circuit. A leak in either heating circuit will not result in the 1000lt buffer draining into the house.
The system works well and is easy to keep an eye on, I've no doubt outright efficiency could be improved somewhat and would look at weather compensation as my first choice if changes are made.
Posted By: djhOne other point to keep in mind about PHE is that they have lots of small passages, so they need clean feeds of water. I'd think about filtering them, as well as isolation valves or other arrangements to flush the PHE when necessary.
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