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How to detect hot waste water - thermal glue


readiescards

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I wish to detect when the bath/shower plastic drain pipe has warm waste water running through it.

I don't need to accurately know the temperature of the water simple that it is present/not present.

 

My first thoughts are to attach a DS18B20 temperature probe to the underside of the white plastic waste pipe using some sort of thermally conductive glue (any glue recommendations?) and look for a temperature change with a RPi.  

 

Maybe that is over kill, any better ideas please

 

Oh and do metal waste water pipes exist?

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55 minutes ago, readiescards said:

Oh and do metal waste water pipes exist?

 

Yep - waste used to be done in Copper and JTM still do it in some big sizes. If you just want a short length of it though eBay is probably

cheaper 

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Usually the heat recovery pipework is connected to say a shower outlet, the cold feed to the shower passes through the heat recovery system. So using the shower operates the heat recovery. In that way you don't need and sensors or valves, other than the user operated shower valves.

 

Edited by Triassic
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1 hour ago, readiescards said:

My first thoughts are to attach a DS18B20 temperature probe to the underside of the white plastic waste pipe using some sort of thermally conductive glue (any glue recommendations?) and look for a temperature change with a RPi.  

That seems the easy approach, silicone should bond it.  You can get them already pre-wired and waterproof. There is code to sense when the temperature changes too.

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54 minutes ago, PeterW said:

 

Yep - waste used to be done in Copper and JTM still do it in some big sizes. If you just want a short length of it though eBay is probably

cheaper 

 

I was in a pub recently, taking a leak, and noticed all the 40-50mm sized waste pipes were in copper. Not something you see very often.

 

ill take a picture next time if anyone is interested:D 

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2 hours ago, readiescards said:

The reason for doing this is log a bath/shower event occurred and maybe drive the mvhr to boost mode.

 

Fyi I definitely don't want boost mode until the bath is draining -ruins the thinking time

 

Why not use a Humidity sensor ?

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The simplest way to do this might be to use a cheap thermal switch bonded to the waste pipe and fed to the MVHR dry contact boost connection.  Something like this:  http://www.ebay.co.uk/itm/KSD-9700-Temperature-Switch-Thermostat-Thermal-Protectors-20-and-25-degrees-/281790336437?var=&hash=item419c034db5:m:mQq9kyBHVG4C7euaGe1_h1g  They are out of stock of the normally open ones you would want, but a 25 deg C normally open thermal switch should do the job OK.

 

Edited to add:

 

Alternatively, if you don't mind running a 12V supply nearby and want adjustment, then the cheap thermostat units from China are pretty versatile, have dry contacts and are adjustable over a wide range: http://www.ebay.co.uk/itm/Hot-DC-12V-Digital-LED-Thermostat-Temperature-Control-Switch-Module-XH-W1209-TC-/391659881408?hash=item5b30bf83c0:g:95sAAOSwA3dYXVNl

Edited by JSHarris
added more info
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39 minutes ago, readiescards said:

Would epoxy resin make a suitable thermal conductive bond? 

 

 

It would, but it doesn't bond well to PVC, whereas stuff like neutral cure silicone does (most acetoxy cure silicones don't bond that well, I've found).  Some neutral cure silicones, and modified silicone polymers (like CT1) will bond well to almost anything.  I've been impressed with the way Dow Corning 799 bonds to PVC in particular, as it's a fairly cheap and readily available sealant/adhesive that seems to be a good all-rounder, despite being primarily intended as a glazing sealant.

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