POTTERTON PERFORMA 28i hot water problem.
- Thread starter Jordylee
- Start date
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I want to learn. Can you explain in layman’s terms what it all means.
You obviously know what Reynolds number is, I don’t. I see resistance to flow of liquid, gas or electrons as similar to differential created by the driver, be it a pump or pressure created by other means
The manufacturers of the plate heat exchangers design for turbulent flow to increase the heat exchange between the two mediums, turbulent flow increases the resistance to flow, so what you see as a short circuit across the plate is more like half the pump output to drive the primary water through it.
Picasso, I am aware the the plates are corrugated to increase the surface area. This corrugation will make the water flow dizzy by the time it exits from the Phex.
You have not answered my query ie, parralel plates will reduce the effective resistance.
The pump, if pushing water through the single plate gap will be under heavy stress
Through 20 gaps, my understanding is, the pump will have easier time not under greater stress.
Where does it say the Phex is designed for turbulent flow. Surely laminar flow will increase efficiency of the unit as turbulent flow will ‘break’ the water hence transfer of heat will be reduced. Corrugations are for increase of surface area just like air cooled engine on motorbike
I am not knocking your knowledge, want to know more.
You have not answered my query ie, parralel plates will reduce the effective resistance.
The pump, if pushing water through the single plate gap will be under heavy stress
Through 20 gaps, my understanding is, the pump will have easier time not under greater stress.
Where does it say the Phex is designed for turbulent flow. Surely laminar flow will increase efficiency of the unit as turbulent flow will ‘break’ the water hence transfer of heat will be reduced. Corrugations are for increase of surface area just like air cooled engine on motorbike
I am not knocking your knowledge, want to know more.
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Have a read of this...Plate heat exchanger principle - SWEP Heat exchangers (heat-exchangers.uk).
Picasso, that article right off says what I have been harping on about
Pressure losses can be reduced by adding the number of plates: doubling the number of plates will reduce the pressure losses to a quarter.
Will read and digest the article, thank you.
Will see if it implies total resistance of the PHex is greater than radiator circuit
One thing for SHURE, what I have been bleating about is counter to your statement that plate heat exchanger has greater resistance to flow.
Attended a Baxi 105e where the pump was weak. The heating functioned fine but flow manifold failed to activate ie pin ejected but not enough to make the microswitch. With greater resistance of heating circuit the pump differential was sufficient to positively energise the switch. Not so for hot water as due to much lower differential across the pump.
Once more thanks fir the link
As in all things mechanical there is a compromise between size, cost, resistance to flow , efficiency ect, if you read the link I posted you will see the average plate has a head loss of 20 to 40 kpa, that is 2 to 4 metres in old money.
What is the head loss in a house where the radiators are around 15-18kW
why would the Baxi 105e in question (where plates are used to heat water as you know) exhibit the HW loop as lower resistance than the heating loop
why would the Baxi 105e in question (where plates are used to heat water as you know) exhibit the HW loop as lower resistance than the heating loop
Thanks everyone for the replies.
It actually turned out to be the Automatic By-Pass valve that sits behind the DHW diaphragm on 28i. So even though the main diverter valve assembly had been replaced and the Pressure Differential Valve was working and switching to hot water, the boiler was only heating the water in the pre heat store. The tell-tale sign was the auto bypass pipe and the CH return getting hot whilst on DWH.
Complete new valve @ £70 and all working fine.
Happy days
It actually turned out to be the Automatic By-Pass valve that sits behind the DHW diaphragm on 28i. So even though the main diverter valve assembly had been replaced and the Pressure Differential Valve was working and switching to hot water, the boiler was only heating the water in the pre heat store. The tell-tale sign was the auto bypass pipe and the CH return getting hot whilst on DWH.
Complete new valve @ £70 and all working fine.
Happy days
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