PHPP: DHW sheet questions...

[Markus Kolb]

I'm working on the DHW sheet for our current project and am a little foggy on the fine-points of this part of the PHPP:

1. I'm pretty sure the first part, titled 'Space Heat Distribution' is just for that – distribution lines for a hydronic heating system (whether it's feeding radiators, floors, or a water-to-air heat exchanger, or whatever).

2. However, under 'DHW Distribution and Storage' there are two sections; one is for circulation pipes, the other one for individual runs. For the former, the suggested design flow temperature is 140°F, which is rather hot for DHW (i.e. potable water), which would sort of seem to indicate that these circulating runs are for space heating as well. Yes, no? I suppose they could be for hot water circulation systems – the kind that make sure the hot water is hot right away when you turn on the faucet – but I'd find this rather surprising. What gives?

3. The second part of 'DHW Distribution and Storage' does clearly seem to be for the DHW runs to the fixtures, and I assume this means any fixture that uses hot water (whether lav, sink, tub, or shower). And it looks like you have to count the full distance to the water heater from each fixture individually, regardless of how they're plumbed, or whether you're talking about fixtures in the same bathroom, correct?

Any clarifications are much appreciated!

Cheers,

Markus

[GnormanTheGnome]

I see that there was a recommendation in Europe to limit the hot water to 50deg C in December of 2010 to prevent scald injuries for kids (that's 122deg F).  It is possible that the norm when this version of the PHPP was created was to have a higher water temperature as we once did in the US.  Perhaps that is the reasoning for the 140deg avg.  (Just a guess.)

My understanding of the DHW worksheet (from someone who has not yet submitted a PHPP):

http://www.smallplanetworkshop.com/small-planet-blog/2012/3/6/the-abcs-of-the-phpp-part-11-dhw-hot-flashes-and-cold-flushe.html 

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[Adam Cohen]

Markus, the middle section is to be used if you have a circulating DHW loop.  You do not enter anything in there if you have a typical non-circ. DHW system.  Also you need to enter the temp and PSI value in that section for the DHW to calc.

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Adam Cohen
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[Graham S. Wright]

1.  Correct, the top part is for hydronic space heating.  The relevant pipe lengths are up to the point where the system is intended to deliver heat, that is, not including the pipes in the radiators or in-floor itself.  

2.  Yes, that is to account for a DHW recirc system, the kind to make sure the hot water is right there.

3.  Yes, per the PHPP manual 24.3.2, the pipe lengths are effectively to be counted as if they are home runs to each fixture.

[Rob Harrison AIA]

I would imagine, also, that this (2) is for a recirc system with continuous looping of hot water, where the pipe acts as a radiator. A system like the Metlund D'MAND for example, which pumps water only when necessary, I wouldn't think would count.

Rob Harrison AIA

HARRISON architects

1402 Third Avenue  Suite 515

Seattle, WA  98101-2120

206.956.0883

http://twitter.com/#!/robharrisonAIA

http://harrisonarchitects.com/

lyrical sustainable design  ::  passive house plus

[Markus Kolb]

Thanks for everyone's replies! I did have a chance to check the German PHPP manual, and yes, they're figuring the DHW (non-space heating) circulation temp at 60°C – don't want my toddler turning on that hot water tap! Perhaps the circulating runs are also more commonly found in European multifamily projects for DHW distribution to individual dwelling units...

Cheers,

Markus