Vaillant ecoTec 937 Boiler

[gonzoelec]

Hi all again,

Well have run the test on the CW and got a flow of 17.14 Lpm as it took 3.5sec to fill a 1lt bottle, the pressure was about 5Bar, so is this good or bad for the Vaillant ectoTec Plus 824 that I was looking at and will that be good enough to fill two baths at the sametime as well as doing the washing up or would I be over running the supply?? or should I just put a time delay on the two girls lol.

Thanks again for all of your help you have all been great with your replys.

thanks again


Dave ;0)

 

[D_Hailsham]

Until the store is depleted the boiler will give about 20 li/min.

But that's does not mean the flow rate from the mains has to be 20 litres/min, as part of the flow comes from the mains and the rest from the store.

The store hold 15 litres of water at 50°C or 65°C. Assuming it is held at 65°C, the boiler will have to provide 185 litres at a temperature of 42°C to give a total of 200 litres in ten minutes. Provided the cold water temperature is not below 7°C, this is possible. That assumes the store is not replenished until the tap has been turned off.

The recommended maximum safe water temperature is 44°C for a bath and 41°C for a shower.

However you work it out, there is no point providing cold water at a higher rate than 15 litres/minute. If you do, all that will happen is the temperature rise will be less. That may be OK in the summer, when the cold water may be at 20°C and you only have to raise it by 15-20°C, but in the winter when the water may be at 5°C.

I would not like to bath or shower with the hot water at 32°C (a 37kw boiler will raise the temperature by 27°C if the flow rate is 20l/min). So you turn the tap down to reduce the flow rate and increase the water temperature.

 

[morrismini]

Hi all again,

Well have run the test on the CW and got a flow of 17.14 Lpm as it took 3.5sec to fill a 1lt bottle, the pressure was about 5Bar, so is this good or bad for the Vaillant ectoTec Plus 824 that I was looking at and will that be good enough to fill two baths at the sametime as well as doing the washing up or would I be over running the supply?? or should I just put a time delay on the two girls lol.

I would do it filling a bucket rather than a 1 litre bottle. When filling a bucket you may find it is around 20 litres a minute. You could improve flow by replacing the maintap to a full bore. It is borderline if you reach 20 litres a minute for what you want. Having 22mm pipe to the cold inlet of the combi will improve matters again.

A 824 will not do two bathrooms, well not together. You need to have two showers running at the same time and do not fill two baths at the same time. Few homes do. The 824 will struggle with two showers. You need a 40 kilowatt combi at least.

 

[morrismini]

..edit

 

[Agile]

Until the store is depleted the boiler will give about 20 li/min.

But that's does not mean the flow rate from the mains has to be 20 litres/min, as part of the flow comes from the mains and the rest from the store.

That is what happens if you try to give advice based on reading specifications without any practical knowledge of the appliance and how they work!

The reality is that the mains pressure is the only driving force in providing the water flow through the boiler ( that includes from the store ) and you only get out what you put in!

The store is only a store and not an accumulator charged with gas or pumped.

To get 20li/min out you have to put in 20 li/min !

Tony

 

[gonzoelec]

Hi all again,

This will be the last post from home as i've got to go to work in a min, so just redid the test and with a bucket and the CW filled a 12lt bucket in 35sec so from my calculations that means that the flow rate is 20lt/min, I see what you are saying about two baths being run at the same time but i was looking at worse case may be I should be looking at a more like the two girls having a shower at the sametime and me doing the washing up. if i get a 40Kw boiler then would this be running effic. with a small CH that is in the house only 11-16Kw CH (calculated), sorry if i'm coming over a bit thick on this.
Thanks for all of your help and your speedy replys.

You are all very helpfull with your posts

Thanks

Dave ;0)

 

[Agile]

You have only measured the open pipe flow rate.

What you get through the boiler and shower head(s) will be less.

It is a good flow rate though and with minor upgrades like a full flow stopcock and 22 mm to the storage combi or an unvented cylinder it will probably be adequate.

Tony

 

[doitall]

An unvented cylinder powered by an an Advanta 18s will give you a much better system, and cost considerably less to run than a 40Kw monster.

Anything above 1 bathroom then forget a combi, even if it will supply the how water, it's never going to modulate down to match the heating load.

Perhaps more important is two girls in the house when it breaks down and you find you have no back-up hot water.

 

[morrismini]

Hi all again,

This will be the last post from home as i've got to go to work in a min, so just redid the test and with a bucket and the CW filled a 12lt bucket in 35sec so from my calculations that means that the flow rate is 20lt/min, I see what you are saying about two baths being run at the same time but i was looking at worse case may be I should be looking at a more like the two girls having a shower at the sametime and me doing the washing up. if i get a 40Kw boiler then would this be running effic. with a small CH that is in the house only 11-16Kw CH (calculated), sorry if i'm coming over a bit thick on this.
Thanks for all of your help and your speedy replys.

You are all very helpfull with your posts

Thanks

Dave ;0)

Yes, that is better. A full bore 22mm stoptap and 22mm to the combi will improve matters. A 40 kilowatt Worcester-B will give 17 litre a minute and an avantaplus 39C about the same, 16-17 litres per min. That will do two showers.

Have 22mm to the combi inlet. Tee off at the stoptap and have the cold off these with isolators to restrict flow to toilets and w/machines. Take the cold to the showers off the cold inlet pipe just before the combi inlet. Do not have one 15mm pipe wind through the house and all tee off it.

There is no need to put a pressure reducer on the cold supply.

 

[Agile]

A person in the trade calls them a stopcock !

A homeowner might call them a stoptap !

 

[gas4you]

If you really have 5 Bar pressure, I would fit a PBV after your stopcock, as this will then balance your hot & cold supply's.

 

[morrismini]

A person in the trade calls them a stopcock !

Is this the trade you are illegally operating in?

 

[morrismini]

If you really have 5 Bar pressure, I would fit a PBV after your stopcock, as this will then balance your hot & cold supply's.

I would only put one at the shower mixer. Many showers have them built into the mixer.

 

[Agile]

I would fit a PRV as 5 Bar is inconviently high for taps.

In fact I would fit two, one for CH and a second one set rather higher for the DHW as the slight pressure differential would help to overcome the pressure loss throught the boiler. Perhaps at 2.0 Bar and 2.5 Bar respectively.

Tony

 

[morrismini]

I would fit a PRV as 5 Bar is inconviently high for taps.

In fact I would fit two, one for CH and a second one set rather higher for the DHW as the slight pressure differential would help to overcome the pressure loss throught the boiler. Perhaps at 2.0 Bar and 2.5 Bar respectively.

Tony

Two Pressure reducing valves? How odd. Flow restricters can be put on taps and pipe lines, which are cheap to buy.

5 bar is not that high.

I can see why the others were getting at you. That is real appalling advice.