Help with Solar Install

[lotus]

A couple of questions we need help with!

1. Is it ok to fit the circulation pump at out of the tank before the expansion vessel?

2. The reflector clips on the install instructions are plastic, they are now metal how do they fit?

3. Does the air vent need to be on the hot or cold side of the panel?

Thanks guys

[Amaterasu]

Hi and welcome....

Here are my answers to your questions

1. Pump siting
The general consensus is that the pump should be fitted after the PV ( in terms of flow around the system).
In simple terms this means that water flows past the Pressure vessel before it reaches the inlet side of the pump.

2. I normally assemble the reflectors on the ground in the following manner -
Insert the steel bolt through the reflector so that the head of the bolt is on the inside of the V section of the reflector.
Place U shaped item over the thread so that the open side of the U is facing the ouside of the V section
Wind on the nut so that it is about a 1/4" in from the end of the bolt.

When placing the reflectors into the panel bring each one in from behind the tubes (eg close to the roof tiles) with the V section uppermost - so that it fits between 2 tubes.
Lift the U section clip and turn so that it spans the 2 tubes.
If you have wound the nut on the correct amount that should be it.
Adjust the nut so that the reflector does not feel either loose or under too much strain.

I am amazed that they manage to remain in place, but they do. I recorded a 56mph gust last winter and they all survived!

3. There is much discussion on the need for air vents of any description - I suggest you do a quick search on the phrase "air vent" and then make up your own mind

Cheers

[mick]

Sorry Geoff (Amaterasu) but I beg to differ re: siting of EV. By my reckonimg there should be nothing between the EV and the panel(s) nor should there be any means of isolating it from the panels such as a check valve or isolation valve. So, going up from the cylinder on the return (cool water back to panel) side it should be - cylinder, pump + allied valves, check valve, EV, PRV, panel. Of course, they are not all next to each other but the middle four can be grouped fairly close together leaving a good vertical distance between the EV and the panel to keep it out of the stagnation area.

While on this topic of placing of components, the EV itself should ideally be on the end of a downwards spur with the entry point uppermost so that there is a dead leg of cooler water again to protect the EV in periods of stagnation. (I drew a diagram but cannot find a way to post it!)

Mick

[dinitro]

Hi Mick

Think non linear.

this is a loop so you flow to the EV in both directions

I have cylinder, EV + PRV, pump, non return, panel

if you think about it panel is connected via cylinder to EV

I think the idea is that you do not get full heat from the panel going to the EV and you do not have
the pump pushing directly against the EV.

dinitro

[Amaterasu]

My recollections of basic hydraulics states that pressure is equal throughout a sealed system, the pump merely pushes that pressure around the pipework.
Pressure will always attempt to escape and revert to equilibrium with standard pressure (atmospheric).

Which is why we get leaks from joints.

The PRV is a specialised type of joint that is designed to open (and release fluid) when the pressure in the pipework exceeds a preset value.

The PRV has no concept of where that pressure comes from.

Provided that there are no (closed) valves between at least one side of the panel and the PRV then it will vent at the appropriate time.

The reason I place the pump where I do is to assist with filling and bleeding, there being a slight lowering of pressure on the inlet side of the pump.
DHW pumps are not self priming and therfore are not capable of "lifting water" so there is no potential for damage to the EV by applying a negative pressure to the underside of the membrane.
 

[Antman]

My understanding is that it's a matter of the difference between static and dynamic pressure.

If there was no pump then arguably it does not matter where the EV is located.

However, you should not have the EV located directly after the pump since dynamically the pump will be trying to pump against the EV pressure. In some circumstances this can reduce the effectiveness of the pump.

With the EV before the pump, it will assist the pump flow against pipe pressure losses by creating a positive (dynamic) pressure on the pump.

Antman

[O MidKnight]

OK  I am on the fence - so far

Grant show a pic with the ev connection at the bottom and after the pump

Thermomax show a pic with the ev connection at the bottom and after the pump

Worcester show a pic  with the ev connection at the top and after the pump

Solheat show a pic with the ev connection at the bottom and before the pump

Viessmann show a pic with connection at the top and after the pump

RWC  show a pic with connection at the bottom and before the pump

Flexcon  manfacturers show connection at the top and  before the pump

[mick]

Sorry Geoff (Amaterasu) - I cheated! The bit about having nothing between the panel and the EV is not actually 'my reckoning' but a German solar regulation.

Many layouts, including dinitro's, site the EV below the pump but the check valve above the pump. This means that during stagnation steam can only go one way (unless the check valve is so near the panel it gets the steam straight away - it may, depending on type, then not react to it), down the return (hot) side. For a given volume of steam that means it would travel twice as far down into the solar loop. It also means that any residual water on the flow (cooler) side cannot be pushed back but trickles forward to produce more steam. Now I accept that the German regulation, which also demands at least 50% of the capacity of the system is between the panel and the EV, is born from the predominantly oversized, flat plate systems fitted there, but you can see the logic of it.

As for the pump's position in relation to the EV, if the EV is on a dead leg, and noting the basic hydraulics priciples quoted above, there should be no pressure differentiation caused by the pump even at start up, these pumps are not really pumps but impellors that induce the water to flow rather than force it like a piston or hydrovane pump, indeed, water can easily flow through a stationary pump.

Hope that clarifies (and, perhaps, justifies) my earlier observations.

Mick.

[O MidKnight]

OK   can someone explain why the pressure showing on the gauge sometimes rises when the  pump runs and on other systems it falls when the pump runs. I am sure this is in direct relationship to the expansion vessel and the pump configuation.

Expansion - pump - gauge = rise in qauge pressure when pump running

Guage - pump - expansion = fall in gauge pressure when pump running

What about expansion - gauge - pump?  Or gauge - expansion - pump?

Antman may well be correct that the expansion vessel situated before the pump is the best position regarding pipe life

[Amaterasu]

Pumping and pressure.
When i studied pumps and primers as part of my fire service examinations I had a load of physics included, which I tended to ignore as I was more concerned about practical issues.
However as time progresses and the need to apply practical pumping skills has diminished all I am left with is the physics.

A pump is purely a means of imparting energy to a fluid, if that energy is contained within a tube with an open end then the energy is transferred into pressure which then attempts to escape out the end of the tube. From that point on you can play with all manner of variables to modify flow rates and pressure, the latter as measured at the pump or the nozzle or at any point in between.

In a solar system the circuit is not open at one end.
It has a positive pressure applied by the use of a Pressure Vessel, but this is a function of boyles law, to increase the boiling point of the fluid it plays no part in the movement of fluid around the system as the pressure is equal all around the system when the pump is inactive..

When the pump starts it imparts energy to the fluid, as there is no open end the only other option is to escape from the source of energy (the pump) in the direction it is pushing.

Therefore if there is a positive pressure on the flow side of the pump there will be a slighlty lower pressure on the inlet side of the pump. Which would explain the differences observed by O Midnight.
As has already been mentioned before in this thread CH pumps are not displacement pumps, which means they cannot create a vacuum on their inlet side and suck water into their inlet. If they did then the pressure difference between inlet side and flow side would be much greater.

Imagine the oar of a rowing boat, when it is on its power stroke. If it would be possible to measure pressure on either side of the blade there would be positive pressure on the side that was pushing and a lower pressure on the back of the blade

[Flamethrower_]

Hi All,

If my  memory serves me right many moons ago.

I was actually corrected by college lecturer, that central heating 'pumps' are not pumps and it is a misnomer to call them that.
He then proceed to say, that the correct terminology being it is a centrifugal impeller as it only pushes the water in a circuit and cannot lift it outside of a circuit.

( I knew that bit of useless information would come in handy one day )

Rob

[Amaterasu]

Flamethrower2.

Hmmm ....... sorry to say it but your lecturer was wrong, a pump is a device that imparts energy to a fluid for the purpose of moving that fluid. Simple as that.
A central heating pump is a centrigual pump, the same type as that used by fire engines.
A typical Fire Service pump is easily capable of delivering 500 gallons / minute at 60psi or 2250 litres at 4 bar (whichever you please!). This would mean that you would empty the tank of water carried on the vehicle in a minute.
To overcome this problem highpressure hosereels were deveolped which combined with some devilish pump trickery raised pressures to 300psi (20bar). At these pressures it is possible to change a jet of water to a fog which increases the ability to wet a surface and hence increase cooling. The jet reaction is something to be experienced!

Anyway I digress .....

Here is the Wikipedia definition of the same - http://en.wikipedia.org/wiki/Pump

"A pump is a device used to move liquids or slurries. A pump moves liquids from lower pressure to higher pressure, and overcomes this difference in pressure by adding energy to the system (such as a water system). A gas pump is generally called a compressor, except in very low pressure-rise applications, such as in heating, ventilating, and air-conditioning, where the operative equipment consists of fans or blowers.

Pumps work by using mechanical forces to push the material, either by physically lifting, or by the force of compression."

[Flamethrower_]

Amatersu,

Thanks Geoff its good to get the right information eventually, just makes me wonder sometimes what is being told to the masses out there
Who is right and who is wrong especially from so called establishment!

[mick]

Hi all,

I hadn't meant to raise a lengthy (interesting) discussion about thermodynamics, nor to challenge those better informed than myself (re: formal study of such things). And I have to concede that for any pump (including impellers) there must be some variation between the suck or feed side and the blow side or nothing would move. But in Amaterasu's fire pump, as in a jet engine, we are talking serious speeds of both impeller and medium, although if an EV was fitted, as in aeronautical hydraulic systems, the precharge would match the design pressure of the system so would push out the charge on shutdown and take it up on start up (I would need to research that a bit more but have it from two airline captains!)

But in our low pressure, low speed systems it will be so small as to make no difference - on the three systems I have personally installed, all with the pressure gauge after the pump, the observed variation between stationary and 100% pump speed is not greater than 0.1 bar, maybe 0.15 on the one with the pressure gauge very close to the pump (in a solar pump station). Except where a pump is either very fierce or very intermittent I still cannot get my head round how the EV will play any part beyond, perhaps, a slight pulse on start up as it experiences the slight change in pressure (what it is there for, after all).

None of that alters my conclusions re:the positioning of the check valve in relation to the panel and the EV. It is normal practice, I believe, to place the check valve, especially spring loaded ones, above the pump so that the positive pressure of the pump opens it. The check valve will prevent liquid from flowing back down the flow side of the loop whether by thermosiphon or push from stagnation steam. If the EV is below the check valve, the liquid and steam can only go one way, the long way via the cylinder, etc, penetrating deeper down the system.

Further, if the EV is branched off low down then it is difficult to arrange a downward branch to protect it from hot liquid, again via thermosiphon. With the EV branch higher up, and therefore above the pump for practical reasons, there can be a good downward drop to both insulate the EV from hot liquid and to make it easilty accessible for adjustment, etc. Part of the trouble, I suspect, is Reliance's pressure group / fitting kit - I don't use it so can have separate components with the PRV / EV branch in a convenient place to exhaust, the pressure gauge as near to eye level as poss, and the EV as above.

So I stand by my formula even if, as seems, my theoretical justification can be shot down. Much of what I am advocating is on the IEA-SHC document posted in the installer area http://www.iea-shc.org/outputs/task26/A_Hausner_Stagnation.pdf but also in similar continental studies elsewhere.

Power to all your elbows,

Mick.

[O MidKnight]

Mick I have just had another look at the IEA-SHC document. It seems pretty comprehensive to me.