How to calculate a cold water storage for 144L Hot water cylinder?

[totcambiu]

Hi guys.

Im desperate for a professional advice. I have recently moved to a new flat where I have a problem with my hot water running out very quickly. The plumber boy provided by the landlady made several visits to no avail. First blaming on the scale buildup, then on a faulty thermostat but nothing have helped so far.

Problem: When I try to fill the bath with hot water ONLY. I'm able to fill 60L of hot water and then water start very quickly but gradually running cold. I have no idea how this whole setup works, but if think logically it looks like hot water cylinder is not filled in to its 144L capacity.

Possible problems from my point of view: There is either a air inside the cylinder that blocks the water intake or cold water storage too small for this setup. Ive asked him about air he says that its an open system or something and there is a vent where excess hot water and air goes out back into the cold water storage. It leaves me with the small cold storage tank.

Is there a formula to calculate and adequate cold storage tank capacity for 144L hot water cylinder? or can someone give me a rough estimate? The cold water storage is about 1.60cm high from the floor.


Current cold water storage size (actual water in the box) 39(L)x25(W)x18(H)=17550
17550/1000 =17.5L

Hot water cylinder capacity is 144L (1050x450)

there is also an electric pump that pumps the hot water, because there is not enough pressure otherwise.

any advice will be highly appreciated.

 

[Howsie]

It might be my explanation, but cylinder not heating fully is not an issue here. It gets real hot, i measured it and my kitchen thermometer shows 85C at the tap end. The problem is that the total amount of hot water stored in the cylinder is about 60L. Its like putting a half empty kettle on instead of full one.

85 at the tap?! Get a new thermometer.

 

[totcambiu]

Firstly that storage tank is too small to be feeding a cylinder (sounds like a 4/10 header tank) even if it wasn't pumped if that is infact what it is feeding.

You will never get the full capacity of a cylinder. How is it heated?
If it is by electric immersion the amount of water you get will depend on the length of the immersion.
I presume your cylinder is a 1050mm x 450mm? A std 700mm immersion will only heat around 100 litres of that overall capacity in around 2 hrs (longer if it is scaled up).

Ok but does the FE tank makes a difference? Will the cylinder still be full of water even if the FE tank is small?

 

[totcambiu]

Can you elaborate why? I believe it is an accurate figure, because if is stick it into the boiling water it shows 99c

 

[Whyme]

if it is accurate then its very dangerouse it should only be 60c, if the cylinder isnt full water wont come out of the top pipe. have you got any pics cos i think that will give everybody a better idea of the setup cos its mainly educated guesses if not.

 

[iiplumbing]

Wow mythbusters video

Thats why you need to be certified to deal with unvented tanks!!

Back to OP.

If your hanging a pump off of a hot water cylinder you need a cold water storage capacity of at least 50 gallons (365litres) otherwise you will run out of cold water let alone hot water.


85 degreee hot water wow, what are you trying to do heat your house via the hot water tank, that is soo dangerous almost instant scalding for you and third degree burns for elderly or children

[TD="width: 607, colspan: 2"]

EXPOSURE TIME TO RECEIVE A SEVERE BURN​

[/TD]

[TD="width: 607, colspan: 2, align: center"]

[TD="align: center"] Celsius
Temperature [/TD]
[TD="align: center"] Fahrenheit
Temperature [/TD]
[TD="align: center"] 2 [SUP]nd[/SUP] Degree
Burn
No
Irreversible
Damage [/TD]
[TD="align: center"] 3 [SUP]rd[/SUP] Degree
Burn
Full
Thickness
Injury [/TD]

[TD="align: center"] 45° [/TD]
[TD="align: center"] 113° [/TD]
[TD="align: center"] 2 hours [/TD]
[TD="align: center"] 3 hours [/TD]

[TD="align: center"] 47° [/TD]
[TD="align: center"] 116.6° [/TD]
[TD="align: center"] 20 minutes [/TD]
[TD="align: center"] 45 minutes [/TD]

[TD="align: center"] 48° [/TD]
[TD="align: center"] 118.4° [/TD]
[TD="align: center"] 15 minutes [/TD]
[TD="align: center"] 20 minutes [/TD]

[TD="align: center"] * 49° [/TD]
[TD="align: center"] * 120° [/TD]
[TD="align: center"] 8 minutes [/TD]
[TD="align: center"] 10 minutes [/TD]

[TD="align: center"] 51° [/TD]
[TD="align: center"] 124° [/TD]
[TD="align: center"] 2 minutes [/TD]
[TD="align: center"] 4.2 minutes [/TD]

[TD="align: center"] 55° [/TD]
[TD="align: center"] 131° [/TD]
[TD="align: center"] 17 seconds [/TD]
[TD="align: center"] 30 seconds [/TD]

[TD="align: center"] 60° [/TD]
[TD="align: center"] 140° [/TD]
[TD="align: center"] 3 seconds [/TD]
[TD="align: center"] 5 seconds [/TD]

[/TD]

The questions you are asking fill me full of dread and foreboding, get yourself a professional on it mate before you kill someone, sorry if thats critical but we are here to help and save people from themselves sometimes

Russ

 

[Howsie]

Can you elaborate why? I believe it is an accurate figure, because if is stick it into the boiling water it shows 99c

Because if its that temp it'll tear the skin off of you.

 

[Dannyparty92]

also mains water would be coming out the vent all the time.

 

[snowhead]

2 immersion heaters in the cylinder, Yes?

1 in the top, Yes?
1 in the side low down,Yes?

How are these controlled, do YOU switch them on?
Are they timed?
Is one on Economy 7 (off peak charge) usually the lower one.?
and 1 on normal rate?

 

[aplombier]

How's he got 85c at tap surely cylinder thermostats knock off at 65 c. Something wrong there.