I want to add a wood burner with boiler to my heating system to cut down on the oil used by my existing boiler.

I have followed a number of posts on this forum that discuss Thermal Stores but I am still confused. I understand the basic principle of the store but have not seen the benefits/disadvantages simply explained. I have also not been able to get similar information on the Dunsley Baker Neutralizer, which claims to do a similar job.

Thermal Stores seem to me to require heating to be relatively constant. What if the house was unoccupied during the day and there was a need to heat the house quickly for the evening. Would not there be a significant lag in having to heat up the store before the heat could be supplied for heating? Would a small store minimize this problem? but surely that would compromise the requirement for reasonable amounts of hot water.

Specifically my questions are

What types of heating system design is a Thermal Store the best solution and why?

What design issues govern the size of the store?

How does a Dunsley Baker Neutralizer work?

What are the advantages/disadvantages of Thermal Store re the Dunsley Baker Neutralizer?

Thermal Stores seem to me to require heating to be relatively constant.
: Not correct really. Do you mean heat in or heat out?

What if the house was unoccupied during the day and there was a need to heat the house quickly for the evening. Would not there be a significant lag in having to heat up the store before the heat could be supplied for heating? Would a small store minimize this problem? but surely that would compromise the requirement for reasonable amounts of hot water.
: The point of a store is that it stores heat. They are very good at heating up your house very quickly providing they have stored heat. So the store doesn't ever get cold. Assuming you want heat morning and evening then in the evening your store will still have the vast majority of the heat that it had when you went out in the morning. And it will be topped up by solar if you have solar and its not dim and completely overcast. The issue is more to do with what heat inputs you have and whether they can be on time switches or whether they need manual intervention (i.e. wood stove). Either way a store will be more flexible than a conventional system.

What types of heating system design is a Thermal Store the best solution and why?
: Most systems that would otherwise use a hot water cylinder can benefit from a thermal store.

What design issues govern the size of the store?
1. How much heat you need to store for heating purposes. This is mainly an issue when you have heat inputs from solid fuel boilers/appliances. 2. How much hot water you need over a day.

How does a Dunsley Baker Neutralizer work?
It acts as a hydraulic neutral point. It's nothing complex.

What are the advantages/disadvantages of Thermal Store re the Dunsley Baker Neutralizer?
Warning: My personal view only::: If you have an existing system and want to add a solid fuel appliance then a neutraliser may be appropriate. If you're starting from scratch and / or need a new hot water tank anyway then I can't see why you wouldn't go for a vented thermal store. The store perfoms the functions of the neutraliser and alot more.

Re advantages I'm sure others will chip in, this is pasted and amended from my recent reply to pantasarus:
There are different types of store, fully vented systems are the most flexible in terms of heat in or out but you will need a boiler that will run on a fully vented system (fortunately these are generally the simplest kind). They work really nicely to integrate both rads and UFH, and also will enable your boiler to work at its most efficient as the return temperature can be controlled to ensure its condensing at all times and the boiler burns for longer periods less often, rather than cycling, and if the store is not up to temperature you can still get hot water out within a few minutes of the boiler turning on. And you get lashings of mains pressure hot water. Also the boiler can be smaller than otherwise required. Solar heat input is via a coil (or >1 coil - see previous posts). There are also stores where the main boiler heat input is via a coil, these are less flexible.

Hello Mike

Yes away & some real cash money employment (phew) for a while.

Stratification is lost as soon as the solar coil warms up in nearly all heat stores anyway and, in my very lay opinion, overstated in it importance. Most heat sources will heat stuff by x degrees rather than from say 40 to 50 but no further so most of the time stratification is irrelevant. My gas boiler heats the top 2/3 of my store, the immersion heats the top 1/2, the solar coil does what it does to the whole 210l and we get usable hot water until the store is blow 40c.

Yes there is much tooth grinding about the general level of insulation on DPS units and the external heat exchanger. It is not hard to insulate the bosses or the exchanger & we put our store in a well insulated airing cupboard, the main loss is now from the pumps same as any other system but less noticeable on non DPS units as they are often not sited next to the water tank (the DPS is festooned in all the bits and bobs for the whole system). I've never lost sleep over the heat losses after some initial concern, fuelled by my solar panel supplier, that my DPS store was why their panels were not working as they claimed, which turned out to be hoakum (or is that Oakham - did you see what I did there?). Heat losses from any normal (DPS/Albion etc) heat store will be fairly high at 80 - 90c unless you encapsulated it in 200mm + of PUR anyway. I always felt that the 'gobbing' and 'watting' over on the well n=known soloar forum about the DPS units lacked subtlety or balance.

S.

Skywalker - Agreed - It just niggles me when I see the temperature rising at the bottom of the tank when I turn on a tap early in the morning because I know that when the solar cuts in it will be a bit less efficient....

Tuna
Also Chelmer heating. Gledhill.
Many many continental manufacturers, especially of (larger) accumulators rather than (smaller) stores

Posted By: Miked2714Hi Skywalker - have you been away, if so welcome back.

Just a quick note about DPS stores, there are pro's and cons to the external plate heat exchanger approach (compared to an internal coil heat exchanger). Pro's are that its very efficient at heating water and can be removed or replaced easily. Cons are (in my view...) you need to consider heat loss (ie consider insulation) from it before installation and when there is a low DHW demand (e.g. a bathroom tap) you lose some heat stratification.

Insulated plate heat exchangers are available.
Stratification can be maintained by using a Danfoss RAVK valve and pipe spreaders.

So, no disadvantages then. :) The real disadvantage is that it uses electricity to run a pump. This may be a disadvantage if running a gravity wood burner, which few people do anyhow.

You can have a hybrid heat bank - a DHW coil and plate heat X. The coil for basins and kitchen taps which do not require high flows. The plate for the bath and shower. Then the DHW pump is not cutting in and out so often. Stratification maintained far more, although that is not an issue with a plate if approached properly.

A plate heat exchanger means a heat bank can act as a combi when exhausted of heat. It produces DHW to the dictates of the boiler burner, so you never run out DHW - ever.

The small plate heat X is the biggest innovation in heating for along time. It has transformed the combi boiler to full two bathroom models from the crock they were 15 years ago.

Clever heating engineers and plumbers use them to great effect in heating cylinders, which means far greater DHW performance and reheat than using an inefficient low slung coil. Using a plate mean DHW is put at the top of the cylinders and heating the cylinder top down, not bottom up like as coil does. That is a massive difference.

A relative of mine installed a body jet shower and of course it exhausted the cylinder pronto. This is common. They contacted me asked for advice being told a new bigger cylinder is needed and they had no space above the existing cylidner to extend.

A plate heat exchanger, bronze pump, flow switch and 3-way diverter valve solved it. The system was made into a DHW priority system, with all the 24kW being sent to the cylinder when DHW is called. The coil was disconnected and a plate and bronze pump fitted. The flow switch was only on the shower line. When the shower was on the boiler immediately came on and directed all its heat to the cylinder and heated it top down. When using other taps the cylinder only acted on the cylinder stat.

It worked. The time in the shower was extended by about 2.5 times, thus making the cylinder "bigger". In reality the energy of the cylinder and boiler were combined .

The setup was similar to this:
http://www.mcdonald-engineers.com/plateflowspec.html

I used a plate to protect a boiler on an old system with cast iron rads. The system was prone to sludge and debris, and could not be cleaned properly. A plate heat X with the boiler flow and return running in and out isolated the boiler from the system. The boiler was always super clean. The boiler was a pressurised system boiler and the rads an open vented loop.

In one heat bank set up I ran the DHW loop around the house to each bathroom, kitchen, etc, It was heavily insulated as 75C water could be running through it. At each bathroom a plate heat exchanger and blending valve was used. It used just one pump - no fresh water secondary circulation bronze pump.

They can get you out of trouble and make matters flexible too.

Tuna: What about the Capito -- http://www.evinox.co.uk/docs/capitosaleslit.pdf

I really like this store -- the only thing it is pressurized, and I want to add a WBS to it. Their literature shows two setups with a solid fuel boiler, one <10kW and one >10kW, both with a direct connection to the pressurized side. Hence I've been following the "other" thread regarding this with great interest.

Posted By: stott1I want to add a wood burner with boiler to my heating system to cut down on the oil used by my existing boiler.

I have followed a number of posts on this forum that discuss Thermal Stores but I am still confused. I understand the basic principle of the store but have not seen the benefits/disadvantages simply explained. I have also not been able to get similar information on the Dunsley Baker Neutralizer, which claims to do a similar job.

The Dunsley Baker Neutralizer is usually a waste of expensive time. It does not do DHW, as a heatr bank/thermal store does.

Thermal Stores seem to me to require heating to be relatively constant. What if the house was unoccupied during the day and there was a need to heat the house quickly for the evening. Would not there be a significant lag in having to heat up the store before the heat could be supplied for heating? Would a small store minimize this problem? but surely that would compromise the requirement for reasonable amounts of hot water.

The key word is "store". It stores heat and when the rads are switched on they are hot within minutes.

What types of heating system design is a Thermal Store the best solution and why?

All types.

What design issues govern the size of the store?

The DHW requirements and the heating too

The heating: A guide, is best to have storage for by 2 the water volume in the rads/UFH. The boiler heats the store and when CH is switched on the rads get hot ASAP, as fast as the pump deliver the water. But there is a buffer of the same volume again. Some say only have by 1.5. This buffer is beneficial in that the boiler is prevented from cycling. Also when the CH is up to temperature, this buffer can be used if there is a large DHW draw-off, say like two baths being run at the same time.

The DHW. This can be easily calculated to what your demands are. Two bathrooms, etc. The plate heat exchanger must be sized too. The larger the better as they are not so sensitive to poor stratification in the cylinder. A large plate heat X will deliver DHW at 50C if the store temp is around 55-57C, or even less. They are very efficient and allow store top operate at lower temperatures to promote boiler condensing efficiencies.

Water Systems

Thanks for all your comments. Are you a heating engineer?

Is it possible to retrofit a DPS store with one of these Danfoss valves. Does it go on the return from the PHEX? Could you post a diagram?

I think they already have a spreader although I'm not sure and there isn't much chance of changing that part anyway.

thanks

Mike

Posted By: Miked2714Water Systems

Thanks for all your comments. Are you a heating engineer?

Is it possible to retrofit a DPS store with one of these Danfoss valves. Does it go on the return from the PHEX? Could you post a diagram?

I think they already have a spreader although I'm not sure and there isn't much chance of changing that part anyway.

thanks

Mike

Mike, DPS use a Danfos RAKV valve to restrict the flow and maintain the DHW
temperature.
http://www.heatweb.com/pdf/DPS/ZedStoreDistrict.pdf

The RAVK senses the DHW outlet (secondary water) and acts on the stored primary water.

Best use a very large plate heat exchanger - 150 kW. These are very efficient and will work at a very low store temperature. This means if stratification is messed up somewhat or the temperature is just low they deliver the DHW.

Stratification is not messed up too much as the volume of water in the cylinder is quite large and the DHW pump pumps the right way. The boiler pump pumps the wrong way but very hot water is pumped into the top of the cylinder, so not a problem.

A pipe spreader can be fitted on the DHW return from the plate. Drill out a compression fitting pipe stop and slide in the pipe. Have an internal pipe stop end. Drill holes in the pipe and have the holes face downwards. All pumps must pump
away from the store.

The bottom of the cylinder can be very cool - 30C, while the top 75C. High
condensing efficiency is guaranteed for most of the re-heat burn.

DPS uses a two-port RAVK valve. You can use a 3-port diverter body and have one
port back to the store and the other back to the other side of the pump. Then the pump will never pump on nothing. If the hot port is closed it pumps back on itself. After the port back to the suction side of the pump fit an in-line adjustable restrictor valve to balance up if need be.

Then only the right amount of water runs through the plate to heat the DHW tro the desired temperature.

Oventrop may do one similar and cheaper.

Hi,

If any one would like some sketches of various set ups I can email them if you send an email to m_up_n at btinternet dot com.

These are just sketches and do not show any safety devices or any thing else they just show the various combinatuions of boilers and tanks etc. In the sketches B = Boiler and could be any boiler / heat source. Obviously in the picture of sealed system it would ahve to be ok for the heat source to be in a sealed system, and some of the combinations would be pointless. I may have missed some combinations and some vital points - they are jsu sketches. I have numbered then so we know which is which.

Cheers, Mike up North

Can't they be attached to a post?

When you add a thermal store you might be able to retain the existing boiler pump and use it to circulate water between the boiler and thermal store. Mention it to DPS. If it's suitable they can probably omit the pump normally supplied fitted to the store for the purpose.

Hi, pasting this in from the tail-end of another thread ... Hope it's considered relevant.
Will start a new thread if not.
Many thanks,
Mike.

Hi, found this thread on a search for "ground heat store" ...
I also have the opportunity to collect heat from the Southwest and push it to the cold North side using low tech under-slate pipework (area available 15 to 30 sqm) and a solar "room". This is intended for use in conjunction with UFH (50 to 55 sqm) and an interseasonal ground heat store.
Does anyone have a sense of what volume I would require to make the ground store a viable part of this set up?
The idea is to link the collectors to the ground store with one loop and the ground store to the insulated UFH slabs with another. Ideally the ground store would be directly underneath and insulated from the floor slab.
Each loop would have differential thermostatic pump control ... (along the lines suggested above by Davidfreeborough but using insulated pile loops rather than air ducts.)
I expect more questions than answers in the first instance!
Mike.