Old Lags or New

I often see pictures of installations posted onto sites like Linkedin by their proud creators. The trouble is given my experience I can often see something wrong from the picture; it might be that the gas meter is fitted too near bends and would therefore be inaccurate, it could be that the boiler would be impossible to service or maybe a simple filter change would require significant dismantling and hours of downtime. But most often it relates to pipework insulation.

When I’ve pointed out that it would not be possible to lag the bare pipe of the picture easily or properly I sometimes get abuse on the lines of “it’s in a domestic premise, Duh!” or “Why would I lag it it’s in the heated space?”.

Now once upon a time that might have been sensible but now when there is a need to avoid wasting energy and thereby minimise carbon emissions is it still?

If pipework is not properly insulated (or the insulation has degraded with time) heat is being lost from the pipe into the space. Was that included by the designer in his heating (or cooling it works the same) calculation? And if it was, have you now decreased the effectiveness of any thermostatic radiator valves and the like by creating an uncontrolled emitter in the room? Are the occupants going to roast? That could be even worse if the pipe carried domestic hotwater which will be required in Summer when the occupied space may actually have the air conditioning running!

Is this a real world problem? Well I have often seen pipework uninsulated in occupied spaces where the inhabitants complain they are too hot even when they have turned the TRV off. I also remember a Leicestershire school I visited once. An old historic school its heating system had originally been coal fired and (like many systems of that time) gravity based. Some of you used to more modern gas and coal systems where the heated water circulates by the action of electric pumps, may not be aware that in the past the natural buoyancy of hotter water over colder was used to move the heat around and avoid pumping (some systems were even before electricity!). This weaker force meant that the distribution pipework had to be MUCH larger and in the school this was 8in diameter cast iron (there are also issues in design and slow response before anyone thinks about using “gravity systems” to save on pumps and electricity).

There had been multiple modifications to the heating over the years with additional radiators, side legs a gas boiler and PUMPING but the main pipework remained the same! The trouble was it still didn’t work properly. The problem was that classrooms near the boiler got warm quickly (and soon overheated) while the ones at the end of the line never got to an acceptable warmth in winter. Effort was spent trying to balance the system to no avail.

So a sensible heating engineer looked at it an realised that once each room was satisfied he needed to drive the heat to the next one. So reasonably he fitted Thermostatic Radiator Valves to all the radiators – to no real success.

What he had failed to allow for was that the surface area of the 8in cast iron pipes passing through the rooms far exceeded that of the (admitted also large) radiators, so isolating them from the water flow made virtually no difference to the heat entering the rooms and the being lost from the pipe. The warm rooms got hotter and the cold rooms still froze.

The answer – insulate the large diameter pipes. (I did suggest using them as sleeves and inserting a smaller preinsulated pipe up their middle but no-one liked that idea!).

Insulation (of pipework and building fabric) looks like an initial unneeded cost that can be avoided – maybe as part of “Value Engineering”- but the admittedly small savings it generates will be there passively through the life of the installation – and retrofitting is EXPENSIVE!

Andy Clarke BSC CEng MEI
And now a committee member of the UKAEE