Navitron Renewable Energy and Sustainability Forum

BIOMASS => General => Topic started by: daveluck_uk on January 18, 2019, 07:58:30 PM

Title: Erratic TRVs
Post by: daveluck_uk on January 18, 2019, 07:58:30 PM

Looks like I have a couple of TRVs that need replacing. They have become very erratic with regards to opening and closing.

All of my rads are bottom fed as is the return. I've seen some installs where either the return or flow utilises one of the top tappings.

What's the current thinking as to which tappings should be used? And what are the advantages of using opposite corners rather than the 2 lower tappings?



Title: Re: Erratic TRVs
Post by: Iain on January 18, 2019, 09:36:41 PM
I now do all mine, top trv, bottom opposite as return. Easier to adjust as you get older!
Seriously I find it a lot easier especially if there is something in front of the rediator, i.e. Sofa.


Title: Re: Erratic TRVs
Post by: Antman on January 19, 2019, 07:39:09 AM
Hi Dave
Some older systems only had a single loop heating pipe with the rads sitting 'on the loop'. These required a top entry flow valve to help promote gravity circulation in the rad otherwise the rad could be slow to heat up.
These systems also had the disadvantage of the rads furthest along got colder water than the first ones as some of the flow had already been through other rads.

On fully pumped systems either method works.

Honeywell TRVs every time for me nowadays. They are the only make I have never had stick - and my own install has had other makes changed twice in 25 years with the exception of two original Honeywells that are still going without ever causing an issue.

Title: Re: Erratic TRVs
Post by: daveluck_uk on January 19, 2019, 12:09:22 PM
Thankyou for the replies. That answers my question and gives me some options.

Title: Re: Erratic TRVs
Post by: andrewellis on January 20, 2019, 12:46:13 PM
I downloaded the brochures from a number of manufacturers when I was doing my radiator sizing for our new GSHP last year.  A few of then had the power output for the different configurations.  A top entry and diagonal opposite bottom corner gave in the order of 10% more power for the same flow/temp input as bottom entry/exit.  I haven't access to the exact figures.  In the end I have bottom entry/exit on the replacements as it was easier.  Later I will be redoing a couple of rooms including taking the walls down.  I will then see if I can get top to bottom past my wife from an aesthetic view point.

Title: Re: Erratic TRVs
Post by: daveluck_uk on January 20, 2019, 03:34:26 PM
 Blimey! 10% is a lot. So did all the manufactures that gave the outputs show an increase?

 Where my system is quite marginal even a 5% increase heat output is probably makes it worthwhile my moving the tapping point when I replace the faulty TRVs.

Title: Re: Erratic TRVs
Post by: andrewellis on January 20, 2019, 03:41:45 PM
 This purmo technical document ( page 101 shows the details of different connection options.  ie connecting as per uk standard means the radiator is 10% less than rated output.

Title: Re: Erratic TRVs
Post by: Philip R on January 20, 2019, 05:22:02 PM
I have all my radiators connected top in bottom opposite out.

The british way is partly out of vanity considerations but reduces radiator output as Andrew has just previously stated.
Bottom in opposite bottom out also restricts achieveable temperature differential without severely curtailing radiator outpit capability.

Top in bottom out allows a much easier to achieve temperature differential and lower return temperature to condensing boiler for better condensing action. i.e an achieveable 5% thermal efficiency gain on the boiler.

Similar gain or better achievable with heat pump as heat source too.

Philip R