Poor pressure on a megaflo??

[Water Systems]

Unfortunately, like all on site measurements the results are difficult to translate from one installation to another because of external influences.

For instance, I could fill my bath much quicker with the hot and cold taps running flat out, rather than just the hot or cold, because of pipework resistances. So a lukewarm bath would fill quicker at my house but not be representative of real use.

I do not have laboratory conditions in my house and offered to take the trouble of making real-life measurements because of the negative and doubting comments of some participants, and their barracking that I was not supplying figures.

If you want to extrapolate some real test data I suggest you contact GAH, in the same manner that you would ask Vaillant on the performance of their combi at 42 delta T rather than the quoted 35 delta T. Taking measurements at a customer installation would not necessarily be representative.

Simon, the example given was in your house. What is the charge pressure of your accumulator? How long to fill the 120 litre bath. That's all. I don't doubt your word at all. I'm sure the system delivers. I'm not into saying it doesn't work.

And talking of figures, much hyperbole has been made in this forum about the relative costs of accumulators from X and Y, I haven't seen much evidence in hard fiscal terms. Someone bought one abroad, but surely you can do better than this?

The Reliance accumulators can be bought at about £300 for 200 litres (100 effective storage), then add a double check valve, PRV, PRV and tundish. That's it. What else? The cost is £450 for the 400 litre unit the last time I looked. So, say approx £500 to 550 for the lot. Having a quality two pump set on your cold tank would be more than £500. Accumulator are a good thing and in some circumstance are the ideal solution for poor mains flow. However a pump set froma tank will operate on any main pressure and flow from a tank which is sized up properly, It can charge up overnight, and size the tank for a days supply of water.

The Reliance accumulators have replaceable diaphragms with on site ease of replacement. An installer who knows the basics can put one together no problem at all. He needs to know a few basic calcs to know the accumulator charge pressure to get the stored water volume. The less the charge pressure the more water stored, but a lower dynamic pressure overall. Most are not capable of this, they only go for packaged solutions.

The same with a heat bank (thermal store with a plate heat X). I educated a self employed installer on these and how to make your own. Now when he gets a job, he orders the parts (a direct cylinder with appropriate tappings) and spends an hour in his garage assembling it. He makes a lot of money doing it this way, forgetting unvented cylinders totally. The average guy will only buy a packaged unit and do whatever the company instructions and tech dept says.

 

[Water Systems]

From the GAH site:

- maximum working pressure 10 bar (shell)
- Maximum operating temperature 70c
- Pre-charge pressure should be set at 1.5 bar below mains static pressure, minimum pre-charge pressure 0.5 bar. This should be carried out before the accumulator is connected to the system
- The accumulator will hold approximately half its total volume in mainss water at mains pressure

So, if the mains is 1.5 bar static, then these can't work. Min charge of vessel is 0.5 bar, so that makes 2 bar minimun mains static pressure.

Simon, you said you could get these to works at 1.5 bar static pressure. Are the above figures ballpark only?

The accumulator can act as a pressure vessel for an unvented cylinder too. Hot water from the cylinder "may" expand into the cold water supply. As the accumulator is on the cold feed this may be unlikely or occur not often.

Trawling posts and info on the web site. Your static mains pressure is 3 bar, so the accumulator is charged to 1.5 bar (web sites says)

That means your 450 accumulator will store 169 litres. It will supply more than that at a decent dynamic pressure as the mains pressure comes in to help when the dynamic pressure in the pipework drops below the 1.5 bar static mains pressure. So just enough to fill two 120 litre baths simultaneously.

I think I got it.

 

[ChrisR]

You are just being pedantic aren't you? In principle they could be made to "work" at any pressure, though rather less well.

I'm not knocking pedantry - can be crucial!

 

[Water Systems]

You are just being pedantic aren't you? In principle they could be made to "work" at any pressure, though rather less well.

I'm not knocking pedantry - can be crucial!

The web site says the accumulator charge pressure is 1.5 bar below mains static pressure. Now that may be because the accumulator is doubling as a cold water accumulator and unvented cylinder expansion vessel. Connected after an unvented cylinder combi valve.

Connecting the accumulator before the combi valve means it stores cold water only and the charge pressure then is not that critical. When doubling as an expansion vessel the charge pressure can't be less than 0.5 bar

Obviously the higher the charge the greater the dynamic pressure at the taps.

Reading the thread, a lot of people really didn't grasp the technical aspects. Now that stupid patent is another matter.