Apprentice needing help, DT for a Combi Plate Heat Exchanger

[swesandrew]

Hi All

I am an apprentice gas engineer and was wondering if anyone can advise on what differential temperature i should have across combi plate heat exchangers.

I am looking for a sort of generic answer if possible to check for blockages etc

Many Thanks in advance

 

[ecowarrior]

I would look at the main flow & return on the plate as that is usually that side of the plate that blocks. If u put a flow temp meter on the flow as it comes out the main h ex going to the plate it will b between 60 - 70 when supplying DHW. When u turn off the DHW u need the latent heat to be dispersed through the bypass via the pump over run. On a perfect day the temp of the flow will not go up and will slowly go down - but if the plate is blocked the heat cant disapate quick enough & the temp will rise. 80 would be my max as a blocked one can easy get over 100 degrees. If u have a temp meter see what happens on your next 10 combi boilers

 

[boilerdoktor]

im sure i was told 20 degrees across the plate heat loss being acceptable.

 

[Agile]

It varies between different boilers and of course with the DHW flow rate.

But typically at max flow rate and a 35 C diff then its usually about 15-20 C.

Tony

 

[petit_pablo]

10-15c temp diff. Much more and your heading down the blocked route.

The HW temp should be the same as the primary return temp if the plates good.

 

[Dan Robinson]

Just ran my bath... 69 in on primary, 33 out.

Guessing 13 or so in on domestic, averaged 53 out, blended to 45. Domestic flow @ 21 l/min, primary? Dunno, Will 15-60 IIRC on slowest speed.

 

[petit_pablo]

Just ran my bath... 69 in on primary, 33 out.

Guessing 13 or so in on domestic, averaged 53 out, blended to 45. Domestic flow @ 21 l/min, primary? Dunno, Will 15-60 IIRC on slowest speed.

Dan thats going to mean fook all to an apprentice

 

[Dan Robinson]

Perraps I should have spell checked it and changed it to Wilo instead will


Still, figures are figures and mine ain't blocked.... shall I give him a hint?