View Full Version : Buffer Tanks - 2 or 4 port connections

29-04-2015, 04:03 AM
Which is best 2 or 4 port and why?

Or does it depend upon the heating load types (e.g. underfloor / simple zone controlled rads)

So under what circumstances would a 2 port connection be best and when woould 4 port connections be best.

Adding to that in each scenario which is the best way to send the call for heat to the HP?

Finally why use a buffer tanks instead of a loss loss header?

29-04-2015, 01:27 PM
Buffer tank will give you added system water content, whereas a low loss header would give hydraulic separation without necessarily increasing the water capacity by any great amount.

02-05-2015, 05:55 PM
Hi Hyperion I understand that , we install buffer tanks and low loss headers, in loads of different environments.

The questions relates to 2 or 4 port port, and then how you manage them.

Example 1 Biomass boiler, long time to come on, like to run for a long time, long time for boiler to cool down - i.e. a large hysteresis, as such boiler manages buffer tank based on top and bottom temperatures and hysteresis on both. Heat load considers buffer as an inexhaustible supply of heat. Call for heat from rads / underfloor merely turns on circulation pump.

Example 2 Ground Source Heat pump (non inverter) supplying mix of underfloor heating and rads, as all heat demands could be shut off recommendation has been install buffer with a 2 port connection so that when heat load is less than production HP will heat up buffer tank and also meets the minumum flow requirements so doesn't get High pressure faults. - Call for heat from heating system

Example 3 Air Source Heat Pump (Inverter controlled) supplying mix of undefloor heating, fan coil and radiant panels, where load could vary from 600W to 10KW,
a) Supplier 1 recommended low loss header with call for heat from heating system
b) Supplier 2 recommends 100 Litre 4 port buffer tank with call for heat from heating system.
c) Supplier 3 recommends 100 Litre 4 port buffer tank with call for heat from buffer tank with single sensor and 6C hysteresis.

SO question is Why the different recommendations re heat pumps, whether its GS or AS? - What's good and bad about each option?

Rob White
03-05-2015, 12:46 AM

With low to large heat loads the buffer will smooth out
the demand and stop short cycling.

With Air sourced the buffer tank is also very useful when
the outside unit goes into defrost mode. With the buffer
vessel the unit can defrost and no noticeable temp difference
in the supplied hot water.

2 port or 4 port?? If 2 port the heat pump has to run to
supply hot water, if 4 port the heat pump can cycle and
so can the hot water demand, independently of each other.

As to why different suppliers recommended different solutions,
I think that comes down to selection choice and product availability??



19-07-2015, 10:37 AM
A 2 pipe will only increase system volume, so you still need a bypass with the minimum flow rate.
A 4 pipe buffer will essentially guarantee flow rate and volume.

If you have a zone controlled system (underfloor) use a 4 pipe
If you have a free flowing system (rads with TRV's) use a 2 pipe