Two flushes to warmer water.

[epsilonGreedy]

Not a serious thread though would someone verify my arithmetic because I was surprised by the low volume of standing water in a mains supply pipe.

 

The other night the onsite temperature plummeted to -7 according to my car dashboard and despite keeping the static caravan central heating on all night, in the morning the toilet refill and washhand cold tap had intermittent ice blockages for a few minutes. The MDPE supply to the static is partly exposed to the elements for 25 meters until it hooks into the street mains water supply. So far ice has self cleared as fresh mains water at ground temperature is pushed through the system.

 

As a defensive measure I have started to flush toilets every few hours to recharge the exposed pipework with warmer water at ground (street mains) temperature and this got me thinking about the volume of 25mm MDPE pipe and how many toilet flushes are needed.

 

http://www.heatwizard.co.uk/pipevolumes.html unhelpfully says the volume of 1m of 25mm MDPE pipe is 0.00033. After a bit of playing with the numbers I assumed this volume is expressed in m3 = 1/3 of a liter per meter of pipe or call it 8.3 liters of standing cold water between my meter and the static caravan.

 

The toilet fitted to the caravan in 2003 is unlikely to be an efficient model so one flush should nearly recharge the 25m meters of exposed pipe.

[Jeremy Harris]

MDPE pipe has a bore of about 20.1mm, so the CSA is about 3.46cm², which gives a volume per m of about 346cc, or 0.346 litres.

[epsilonGreedy]

1 hour ago, JSHarris said:

MDPE pipe has a bore of about 20.1mm, so the CSA is about 3.46cm², which gives a volume per m of about 346cc, or 0.346 litres.

 

 

I have been surprised by the natural insulating properties of MDPE pipe. We have had a permanent ground frost for days and yet the air exposed mains pipe has not suffered more than a few lumpy ice crystals.

 

Given how little water sits in domestic pipe I will be more inclined to purge the system of stagnant water after returning from say a 2 week holiday.

Edited February 1, 2019 by epsilonGreedy

[Jeremy Harris]

Just now, epsilonGreedy said:

 

I have been surprised by the natural insulating properties of MDPE pipe. We have had a permanent ground frost for days and yet the air exposed mains pipe has not suffered more than a few lumpy ice crystals.

 

That's more to do with the relatively high thermal conductivity and heat capacity, of water, I suspect.  Mains water will probably be close to the ground temperature around 1m down, which tends to be between about 6 deg C and 8 deg C in much of the UK.

 

Comparing air and water, air has a heat capacity of around 1,012 J.kg^-1.K^-1 whereas water is around 4,200 J.kg^-1.K^-1 , so for any given cooling condition, water will tend to stay around 4 times warmer after a set period of time than air.  Add in the effect of thermal conductivity from warmer water below ground, up through the pipe filled with water (water is around 23 times more thermally conductive than air) and it's perhaps a bit easier to understand why pipes filled with water can take a long time to get cold enough to freeze.

[scottishjohn]

just cover the pipe with soil/sand ,old carpet anything --even a small amount will make a difference and keeping the snow of it cos the ground below will be trying to heat it up

Edited February 1, 2019 by scottishjohn