Webasto thermotop C Installation Instructions Manual page 18

PLUMBING OPTIONS
WATER (non-pressurised)
All these systems are filled via the header tank with a mixture of 75% Water & 25% Glycol.
Example 1. Gravity system with a one pipe header tank.
By far the simplest gravity fed system.
Quick and easy to fill up with coolant.
The header tank is connected via an equal T piece in the return line of the heating spine within
about 30cm of the coolant pump inlet.
This is the quickest and most cost effective system to install with regards to material costs.
However, it is by far the most onerous system to commission.
The main drawback of installing a one pipe header tank system is the difficulty in removing the
air from a dry system during commissioning.
Example 2. Gravity system with a two pipe header tank.
Similar to the first system but instead of relying on air to naturally travel up one single pipe via a
T piece, this system deliberately circulates water through the header tank to remove large
amounts of air. The tank is plumbed into the system as in example 1 above but instead of the T
piece, the pipe is cut and an elbow is fitted on each end and two pipes are run vertically up to
the header tank.
With this type of arrangement all the large pockets of air will be taken from the system.
There are two problems with this system, firstly, when the visible air bubbles have been
removed there is no reason to waste energy pumping water up to the tank and then back down.
The header tank ends up being a radiator! Secondly, the water turbulence is constantly
introducing micro bubbles into the water. These air bubbles act as an insulator and reduce the
thermal efficiency of the water that's being circulated.
Example 3. Gravity system with a two pipe header tank and bypass valves
The header tank uses two vertical pipes, one in and one out as in the above example
However, the two vertical pipes connect to the spine via 2 Tee pieces.
In between the two Tees, a ball valve is fitted.
The reason for this is to speed up the air purging as in example 2, but to also negate the
formation of micro bubbles.
How it works. When the system is dry and being commissioned we need to get as much air out
of the system as possible so we Close Valve A. This forces the water up into the header tank
and back down to the circulation pump and is a good performance indicator of the air / water
content during the commissioning process. When all the visible air bubbles have been removed
Open Valve A. The micro bubbles will now eventually vent from the water and into the header
tank. As opposed to example 2 the header tank in this system no longer acts as a radiator or
imposes any additional flow resistance.
This is the most efficient non-pressurised header tank system.
Webasto Part Number : 4110310A
Issue No: 02 : 10th November 2010
Matthew Millard
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