GSHP, Bypass and Buffer Vessel

frslam

Hey Guys - when my IVT HT Plus E7 was installed in 2009-10, the installer (my own plumber) added a kind of Bypass and as far as I'm aware - it's an old trick that plumbers have done for decades - left it half open. I guess this was for circulation pumps, so they're never circulating against a closed valve. I have since added a decent sized Buffer vessel, can I close this Bypass now? I notice when the Hot Water is cycling, the pressure gauge attached to this wee Bypass starts to climb by almost half a bar (pressure gauge for the Under-Floor Heating). Could this be a result of the Bypass being half open? The Under-Floor water loses pressure (albeit slowly) because this Bypass is open and Heating the Domestic Water continually affects the pressure of the Heating water. Thanks

Reed_Richards

There is no need for a bypass when heating DHW and no need for a bypass on your central heating if you have a buffer vessel.  If a valve stuck so that water was going to neither the DHW cylinder nor the central heating then my heat pump would detect the lack of flow and turn itself off.  If yours does not do that then the bypass valve would cater for that eventuality.

Modern bypass valves respond to differential pressure between the flow and return so will open more when this becomes higher than the set value.  

frslam

Reed_Richards said:

There is no need for a bypass when heating DHW and no need for a bypass on your central heating if you have a buffer vessel.  If a valve stuck so that water was going to neither the DHW cylinder nor the central heating then my heat pump would detect the lack of flow and turn itself off.  If yours does not do that then the bypass valve would cater for that eventuality.

Modern bypass valves respond to differential pressure between the flow and return so will open more when this becomes higher than the set value.  

Hi, thanks for that. When I say bypass, I don't mean an automatic bypass, it's a small bore pipe linking the flow and return for the under-floor heating (just where the flow/return pipes exit/enter the top of the heat pump). When my system was installed, bypass valves weren't the norm, Ice Energy were focused on Energy usage/saving and the schematic they provided assumed most of my Groundfloor loops to always remain open, keeping a lot of circulating water in the system. My downstairs rooms would get to 25 - 26c, upstairs would reach 20c (plates between joist centres). I had to retrofit a Buffer Tank to allow temperature zoning downstairs. I have a circulation pump outside the heat pump, it's on the flow AFTER the buffer tank, I've set the heat pump internal circulating pump to switch off when the heat pump is not running (default was on) and since I have got no automatic bypass valves on my system, I leave one loop (upstairs bathroom) permanently open. This is because of the circulation pump just after the buffer vessel which runs permanently. I was told by Ice Energy at the time (2010) that this pump runs permanently for the heat pump to continually sense the return water temperature. Would it be viable to retro-fit a bypass valve, preferably close to, but after the external circulation pump? Many Thanks 

Reed_Richards

You can retro-fit a bypass valve wherever you like but I cannot see why it is necessary.  I have a similar set-up to yours with two pumps, but I don't have a bypass valve.  The reason for permanently running the circulation pump on the UFH side of your buffer vessel went away when you installed the buffer vessel.