By Pass Valve

[jc_150]

Hi all in the forum,
I have a 6 radiator Y plan system with pump over run. There are 5 TRV's on the rads and the living room radiator is open at all times. I have now put Hive thermostatic rad valves on all the radiators with TRV's. It works ok, but there is an annoyance because if for example the bathroom radiator calls for heat, the boiler will only fire if the room where the thermostat is (the living room) is at a temperature lower than the boost temperature. This means by default the bathroom and the living room heat until the requirement is met. I was wondering if it is feasable to have fitted a bypass valve of some sort so that when pump over run is on there is somewhere for the water to circulate so that I can then have a TRV fitted to the living room radiator to make the system totally automatic. It was suggested that having a towel rail fitted may be a better idea. Thanks for any replies in advance.
John

 

[John.g]

Hi John,

I have 10 rads, I had 8 on TRVs and 2 in the main living quarters on a roomstat, I have since fitted TRVs to these 2 rads and generally run with the stat turned up "fully" and all the rooms controlling on their TRVs, I only occasionally use the roomstat. I have an oil fired boiler so no need for pump overrun or bypass valve.
You have pump overrun so with all TRVs you will need either a automatic by pass valve (AAV) or a towel rad. AAVs work very well with the old traditional 3 speed circ pumps but not too well (if at all, IMO) with all the A rated pumps as the traditional 3 speed constant curve settings no longer work in that manner for some strange reason resulting in the AAV being either open all the time or shut all the time. You can fit a manual by pass but this will result in a loss in boiler efficiency due to the constant by pass so a towel rad might be your best bet.

 

[John.g]

Assuming you have a gas boiler you also don't want the flow/return temperature differential, deltaT, higher than a very max of 30C, TRVs achieve room control by throttling the water flow which leads to higher deltaTs. Its very unlikely but if all the rads (together) are required to output 1/2 their rated output then the deltaT will be approaching 30C with a boiler flow temp of 65C. Before going any further you might consider turning the room stat up, shutting off one side of any non TRVd rads and just observe the flow/return temps on the boiler.

 

[jc_150]

Hi again,
Thnks for the replies. In case it makes a difference the pump is a grundfos Alpha 2 and I have it set to constant speed 2. The boiler is an open vented condensing boiler. I have orderd a couple of pipe temperature guages so I can do the test that John G suggested. If this goes well I can think about having the job done as I would like all auto. function.
John

 

[jc_150]

Hi again,
Thnks for the replies. In case it makes a difference the pump is a grundfos Alpha 2 and I have it set to constant speed 2. The boiler is an open vented condensing boiler. I have orderd a couple of pipe temperature guages so I can do the test that John G suggested. If this goes well I can think about having the job done as I would like all auto. function.
John

Hi all again
I have now carried out the test that JohnG suggested and all well, the deltaT at the boiler was about 16 degs.C The clip on pipe gauges were a little clumsy so this is not a decimal accuracy reading. I have a plumber coming next Friday to fit the ABV and a Hive thermostatic programable TRV on the only radiator without one. From your experience with my set up is there a best setting for the Grunflos Alpha2 pump such as Auto, P1,P2,C1,C2 to suit the Alpha 2 pump with an ABV. . The manufacturers guides seem to suggest C1 or C2. where an ABV is fitted. I am obviously clueless on this but have become morbidly interested in how it all works and have read lots on it, especially the mid port valve on the system. Tin hat on, so here is what I have worked out. If at the end of each heating cycle that I program I was to program a 15 minute hot water cycle, then if the water was cold enough it would put the valve in water only mode and stay there as it was the last called for request and create a a natural bypass until the next heat cycle and repeat the process and have the fall back of the ABV should the water be up to temperature at the end of the heating cycle and the mid position valve be on heat only. Would this work or should I wait till the pubs open and forget about heating issues. Thanks for any replies in advance
John

 

[John.g]

Presume the programmable TRV doesn't shut the boiler down? and all the heating temperature control is/will be done by the TRVs, if so, when the heating period(s) are over why can't the TRV'd rads take the pump overrun flow?, wasn't the test done with the non TRVd rad shut off and you were still getting 16C deltaT which indicates that one or two are always partially opened.
A ABV is normally a good idea but extremely difficult to set up with the modern circ pumps as I said in post #2 but maybe it can be set up properly and depends on the sensitivity of the ABV as there is admittedly some increase in the CC pump heads with decreasing flow with this particular pump model .
Also changing over to HW heating at the end of the CH period is a good idea IMO.

 

[jc_150]

Presume the programmable TRV doesn't shut the boiler down? and all the heating temperature control is/will be done by the TRVs, if so, when the heating period(s) are over why can't the TRV'd rads take the pump overrun flow?, wasn't the test done with the non TRVd rad shut off and you were still getting 16C deltaT which indicates that one or two are always partially opened.
A ABV is normally a good idea but extremely difficult to set up with the modern circ pumps as I said in post #2 but maybe it can be set up properly and depends on the sensitivity of the ABV as there is admittedly some increase in the CC pump heads with decreasing flow with this particular pump model .
Also changing over to HW heating at the end of the CH period is a good idea IMO.

View attachment 60353

Presume the programmable TRV doesn't shut the boiler down? and all the heating temperature control is/will be done by the TRVs, if so, when the heating period(s) are over why can't the TRV'd rads take the pump overrun flow?, wasn't the test done with the non TRVd rad shut off and you were still getting 16C deltaT which indicates that one or two are always partially opened.
A ABV is normally a good idea but extremely difficult to set up with the modern circ pumps as I said in post #2 but maybe it can be set up properly and depends on the sensitivity of the ABV as there is admittedly some increase in the CC pump heads with decreasing flow with this particular pump model .
Also changing over to HW heating at the end of the CH period is a good idea IMO.

View attachment 60353

In reply to John, Thanks for the continued support with this. With the hive system and programmable TRV's on each rad, from what I have read when the system is switched to "On Demand" mode any rad can call for heat independantly of the heat requirements of other rads. It does this by any rad signalling the thermostat to go into "Boost" mode for 30 minutes until the rads have reached their set temperature, and if not satisfied call for another 30 mins. The requirements for this is obviously a rad has to call for heat and the thermostat and radiator(s) are in an active time period and the room with the thermostat has to be at a lower temperature than the "Boost" temperature which is settable in the app. In my simple mind I am having a bypass valve fitted so that when all the radiators have reached their set temperatures the boiler will still be in a timed process and the the water can circulate via the bypass valve, as well as when the boiler does switch off the over run has somewhere to go. I think the difference in the temperatures that I got may have been that I did not monitor all the radiator temperatures to se if a flow was possible. I think I may be over thinking the whole thing, and the plumber will know exactly what is possible.
John