4 ms·
I don't understand his chart on Page 77 showing the amount of water wasted for the different layouts. He has the Zoned at 12 gallons, and the Manifold at 23 gal
by nkurz 9y ago
I don't understand his chart on Page 77 showing the amount of water wasted for the different layouts. He has the Zoned at 12 gallons, and the Manifold at 23 gallons. The note below says that the "estimate is based on 20 cold starts per day". I'm guessing this means total uses, with some fixtures used more than once (eg, kitchen sink 3 times and lavatories once)? And "cold start" means that it's assumed that the time between uses is such that one always needs to wait for hot water to come all the way from the tank?
The Manifold system is a "home run" with 1/2" to all fixtures except the tub, and the Zoned system is a mix of 3/4" mains and and 1/2" branches. Since the direct run should never be longer than the branched run (right?) how can the system composed of all small pipe waste more water than the system with a mix of small and large pipe? In a cold start measurement, I'd think the Manifold would have to come out ahead for every fixture except the tub, which would be a tie. And thus I'd think that any combination of fixtures would have to come out better, rather than worse.
(I'm not saying this makes the Manifold approach better overall, just that something seems off about this numbers)
- nippoo 9y agoYou're assuming that the water cools instantly and you're always wasting the run from the boiler to the fixtures. This isn't the case: the big advantage of the zoned approach is that the trunk will remain warm if you're using multiple fixtures branched off the same trunk. So if you have a shower while your washer is in use, you only waste that little branch of water, rather than the whole trunk (or the home run in the manifold approach). Or if you wash your hands and have a shower in the same bathroom within half an hour (for example). With the manifold approach, you lose the efficiency savings when you use the sink / washer / shower within half an hour of each other.
- nkurz 9y agoYou're assuming that the water cools instantly and you're always wasting the run from the boiler to the fixtures. No, I'm just assuming that the definition of a "cold start" is that the water is allowed to cool before the next measurement is taken. The alternative (which I agree is common) is a "hot start". The author defines these terms on the box on the bottom left of Page 76 (which I don't seem to be able to copy and paste). Since the chart explicitly says "cold starts", my question/complaint is that as labelled, I can't see how the chart can be correct. I agree that measuring a blend of hot and cold starts is probably a better metric to judge the systems by.