When planning a retrofit, optimising the domestic hot water is often overlooked. The heat source itself may be considered but what about the plumbing? While walls are stripped or partitions being rebuilt is the best time for re plumbing.
This article, unfortunately not using metric measures, explains how to minimise wait time for hot water. Remember that the cold water before it gets hot has been heated once. The energy used to heat it has been lost. You might claim that the lost heat has contributed to space heating, but do you really want space heating in mid summer?
I struggled a little with this wording. I think what you mean is that the cool or cold water which flows initially from the hot tap (until the hot water starts to come through) has been hot once, but has cooled as it has been sitting in the pipe.
For a passive house, new build or retrofit, radial small bore hot water pipework is normal. In the third photo in the linked articel (the one captioned “Larry Weingarten likes to put the hot water manifold…”), the manifold with valves straight on top of the tank looks like a pretty good radiator. The Passive House recommendation to avoid this, is to have a minimum 100mm drop from the tank outlet to the manifold, and to insulate the manifold. See attached diagram: no need to insulate the radial pipes.
You don’t see inline modulating electric heaters talked about much… basically electric showers attached to the pipework. Placed strategically and they could serve a number of far-away units. They use a lot of instantaneous power but then cycle down when the hot water finally arrives.
Another way may be to have a storage system inline, like a SunAmp.
This manifold approach still seems like there would be a lot of wasted pipework for a larger house if the wet rooms and heat source weren’t well placed.
But better to reconsider the layout of hot water pipes and minimise it, imo.
Traditionally the wet rooms are stacked above each other, assisting gravity fed water (hot and cold) and in particular drainage, however there are plenty of exceptions.
As regards the inline hot water, that could be added to this list:
As with most things I imagine the significance of such things as manifold vs branch is project dependant.
One of the reason manifold is uncommon in the uk is that our houses are small, and the benefits would be negligable. I suppose there is a branched manifold option too!
I wonder why they are suggesting there is no need to insulate the branched hot water pipes?
