We installed a DPS GX heat bank a couple of weeks ago. Installation is exactly as per DPS diagrams/instructions except for one detail - the CH pump is fitted on a pipe going vertically up, rather than down. This is because the cylinder and the boiler are both in a cellar, and pretty much at the lowest point in the circuit.
Everything works fine, and the hot water is a miracle of heat exchanger physics, except...
I'm getting really strong gravity circulation on the CH. Strong enough to heat the whole house uncomfortably; mostly because it's not really cold outside, the house is well insulated and there are a couple of towel rails without TRVs, but still it should not happen.
At this moment, there are no zone valves in the CH circuit (may put them in later if TRVs on rads and room thermostats on convectors prove inadequate to control). As I see it, I have 4 options:
- Leave as is, shutting/opening circulation with a manual check valve on the pump every time I need CH to stay off/on. It works, but it's not exactly convenient if you like the house warm when you get up but not during the night, especially with the pump in the (well ventilated) cellar.
- Re-plumb so that pump pipe goes down before it goes up. However, given strength of circulation and circuit layout (practically a straight 6m rise on a 28mm pipe), I doubt that a metre or so of "down" before "up" will stop the flow; the cold mains gets heated by conduction to about 3 metres away, and it's tapped into a colder layer of the heat bank. Also, it's a pain to do given the amount of pipes that are already in the area.
- Insert a non-return valve on the pump flow to introduce some resistance - DPS actually advised in this sense. My concern is that the circulation is quite strong, and the NRV will not offer enough resistance (or if it does, the pump will see too high a load and fail to provide the 60 lpm that I need for the convectors to work properly). I could not find data on pressure loss for NRVs, nor do I have a flow/pressure chart for the pump (Grundfos 25/80) so this may just be me being paranoid.
- Insert a zone valve before or after the pump, wired in parallel with it, so that circulation is effectively shut off unless there is demand for heat from the programmer. This certainly works, but it's relatively expensive (GBP60+), and the motorised valve is a potentially unreliable component.
Has anybody got experience with this situation? Any advice greatly appreciated.
TIA
Davide