Twin buffer tanks in series or parallel

[Keith Hughes]

Hi I'm about to install a 30kw Gasification boiler. I also require 2 x 1000ltr buffer tanks, I've looked at many installations and it's not clear which is the best option series or parallel. Also I'm not sure of the best pipe size between the 2 tanks, the tanks have 1 1/2" connections I was thinking of using 1" pipe work. The main first tank also heats my hot water, the second tank acts as additional storage. What would be the best draw off point for the central heating to make the best usage of the stored heat?

 

[ShaunCorbs]

@Worcester

 

[Worcester]

Hi I'm about to install a 30kw Gasification boiler. I also require 2 x 1000ltr buffer tanks, I've looked at many installations and it's not clear which is the best option series or parallel. Also I'm not sure of the best pipe size between the 2 tanks, the tanks have 1 1/2" connections I was thinking of using 1" pipe work. The main first tank also heats my hot water, the second tank acts as additional storage. What would be the best draw off point for the central heating to make the best usage of the stored heat?

I guess you're not in the UK?

We often configure buffer tanks with mid point loading and 2 (3 point) connections with gasification boilers, you also need weether compensation and fixed temperature compensation valves on the heating circuits.

Consider Tichelmann connection though a properly installed equal pipe parallel (symmetrical connection) system usually performs better.
Piping these up with all the proper controls is not a diy project:

That's 6 hours work for two people between these two photos, (three heat sources, at different temperatures, log, lpg and heat pump, four heat consumers at different temperatures, DHW cylinder, weather compensation for radiators, fixed flow for towel rails and reduced temperature for underfloor heating.
Pipework in the symmetrical connection is millimetre (4o thousands of an inch) perfect.

Check this out: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.666.1060&rep=rep1&type=pdf

Initial testing using the Tichelmann-ring arrangement revealed significant problems associated with balancing the flow through the three heat exchangers. It has been noted in the literature (Peuser, F. A et al., 2002) that this arrangement is extremely sensitive to friction losses through the piping (e.g., surface roughness, solder connections, elbows and other constrictions) that may result in flow imbalance. The non-uniform charging initially observed was also aggravated by the low flow rates through the collector-side charge loop and low pressure drops through the heat exchangers. To remedy this situation, the plumbing arrangement shown in Fig. 4(b) was adopted. Subsequent tests conducted with this arrangement produced significantly improved results with respect to flow balance. A schematic of the parallel multi-tank configuration used for this study is shown in Fig. 5.

 

[Keith Hughes]

Below is the suggested layout from boiler manufacture, I'm English living in Germany, and an ex plumber/solar thermal installer. My two 1000ltr buffer tanks are 5m apart, one of the tanks supplies DHW as well as a buffer. I'm going to link them with 1 1/4" pipe work. There is no underfloor heating just zoned radiators. The only heat source is the boiler. I was also thinking I should have some sort of pump between tanks, for when the tanks are used as heat source.

View attachment Attacksch.jpg

 

[Worcester]

That'll work, it's just a pair of buffer tanks in series.

If I did that. I'd probably take the DHW and Radiator connection and return off before the buffer, that way if everything is cold, as soon as you fire the boiler up you can get heat. Rather than it having to heat xx litres in the top of the buffer.

If that's the drawing from the boiler manufacturer, then I guess they are at the budget / value end as they appear to be missing all the safety controls and isolators from the sketch.

You shouldn't need a pump between the buffers.

To make this work best for you, I would suggest that you get a local heating engineer to design it for your actual property.

 

[kris]

Great advice G, your work pics are top class ,

 

[Keith Hughes]

Hi thank you for the advice, there are many safety controls added just not shown on the basic layout. Because the boiler is lit daily there is never a cold spot at the top of the buffer tank/DHW tank. Also because the heating draw off point is not from the top of the tank there is naturally a storage of hot water at all times.