single family residence in southern calif
single family residence in southern calif
(OP)
Hi All,
I'm an owner/ architect working on my own house in Los Angeles.
It's a multi level hillside house partially buried:

I'm planning 3 zones based on how I predict the house will be occupied.
I'm assuming that a split system is the way to go but I really don't like the fact that cool air & warm air come through the same registers.
Two solutions come to mind:
1. Install duplicate ducting to each conditioned room one high, one low (not really liking this idea).
2. Install radiant flooring for heat and ducting for cooling only (radiant flooring seems excessive and is rare in southern cal).
Any other ideas out there?
Thank you!!
I'm an owner/ architect working on my own house in Los Angeles.
It's a multi level hillside house partially buried:
I'm planning 3 zones based on how I predict the house will be occupied.
I'm assuming that a split system is the way to go but I really don't like the fact that cool air & warm air come through the same registers.
Two solutions come to mind:
1. Install duplicate ducting to each conditioned room one high, one low (not really liking this idea).
2. Install radiant flooring for heat and ducting for cooling only (radiant flooring seems excessive and is rare in southern cal).
Any other ideas out there?
Thank you!!





RE: single family residence in southern calif
knowledge is power
RE: single family residence in southern calif
>>>These fora should not be used to bypass your own in-depth research on the issues that affect you, nor is it intended to be a substitute for appropriate professional assistance within your field or geographical region.>>>
You may have to consult an Engineer who designs heating/cooling systems.
RE: single family residence in southern calif
I've solicited help from a number of engineers in my area and they're either not interested (single family) or they just want to run it through their manual j load calc software as a split system & send me an invoice.
No one seems to want to address the bigger picture, so that's why I posted.
For some reason the image in the original post didn't show so here are a couple of links:
Street View
Ducts!
Thanks again!
RE: single family residence in southern calif
Sure, you could improve performance a bit with separate distribution, but the improvement will likely be imperceptible.
Cooling will dominate I suspect, so I'd design for cooling and take what you get for heating.
As an alternative to completely separate distribution, how about a common distribution system with separate registers only. Switch from high to low distribution with change of operating mode.
Or look into high-pressure distribution systems. It might offset the cost of installing separate conventional duct systems.
Won't all those extra registers be unsightly?
RE: single family residence in southern calif
And of course, hire professional to do calcs and specifications, even if it is not mandated, calcs can save you much on initial investment compared with "rule-of-thumb" sizing.
RE: single family residence in southern calif
Individual dx terminals...sounds similar to "ductless systems?"
Looks like you're replacing ducting with plumbing (which makes my job as an architect easier).
I think something like this would work for the bedrooms w/ compact size, but how about an largish open area w/ multi levels?
RE: single family residence in southern calif
you have number of different indoor units to use, i believe wall parapet units are best for residences, but living rooms might need some other, like concealed, cassette or so.
you still need ducting for ventilation, but ducts will be much smaller.
RE: single family residence in southern calif
LA has a reasonable heating season, not extreme in terms of outdoor design temp, but it is sufficiently long to want to do it right. Radiant floors are super comfortable and quiet, but this will mean a whole new system to buy and maintain if you already have planned a central cooling, hard to justify unless you really want the floor warm through winter. However, if it was my house, I would be looking to heat the floor as I hate the noise of the central air.
I also want to add that decent double glazed windows will do just as much for occupant comfort in all seasons as a well designed HVAC system.
RE: single family residence in southern calif
RE: single family residence in southern calif
The biggest objection I see is stratification. A system optimised for cooling does not do so well for heating because of that.
Hence Mint Juleps comment"Cooling will dominate I suspect, so I'd design for cooling and take what you get for heating."
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: single family residence in southern calif
However, from a practical point of view, there are two reasons why dual ducts are undesirable for me; they take up way more room, and you never heat and cool at the same time, and usually not even during the same season. This would suggest that having a single set of ducts but with two sets of registers might make more sense. One could contemplate even having manual controls that switch between heating and cooling, since there's rarely a time when you need both in the same season. Another reason for not having two sets of ducts would be that you probably are using the same air handler, so mucking with duct sizes and pressure drops will likely drastically ding the efficiency of the air handler, and I certainly can't imagine running two sets of air handlers.
TTFN
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RE: single family residence in southern calif
So yes, design for cooling and build a good house. You'll be fine.
RE: single family residence in southern calif
Seems like a conventionally ducted split system w/ two sets of registers is a reasonable way of dealing w/ the problem.
It's wood frame construction so we can use wall cavities to send air up or down w/in each conditioned space.
Drazen's idea of atomizing the mechanical equipment is a compelling way to keep the ducting down but I worry a bit about more units to buy/maintain.
RE: single family residence in southern calif
Additionally, often the selected stud cavities aren't by default correctly sized for the amount of air that should move through them to be good choices.
The problem with most residential HVAC design is the supply and return distribution system robs the a/c or heat of capacity. You end up spending money to heat or cool ducts, money that should rather go toward controlling space temperatures.
RE: single family residence in southern calif
I think I can design around the shortcomings you're pointing out: In every case this transfer would take place in a sealed duct located between studs, and would occur only on interior walls. In general I'm trying to keep ducts away from the exterior envelope.
RE: single family residence in southern calif
RE: single family residence in southern calif
TTFN
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RE: single family residence in southern calif
This makes it sort of ok for return air, but does not work very well for supply ducts.
However that said it may be one method of sorting out the heating/cooling. Use a diverter flap on the same return duct with two grilles in the space, one high,and one low. The diverter flap would seal off the low grille for cooling, allowing the upper grille to draw. Then while heating open the lower grille and seal the upper.
I believe this is what Mint Julep was saying"" As an alternative to completely separate distribution, how about a common distribution system with separate registers only. Switch from high to low distribution with change of operating mode.""
However I think he was talking about supply ducts.
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: single family residence in southern calif
Anybody...............
RE: single family residence in southern calif
No. It is where people often choose to place ducts that create problems.
* Ducts in attics = HVAC capacity loss and possible building pressure concerns due to leakage.
* Using building structural cavities as air conduits = same leakage and capacity concerns.
* Inferior duct design = capacity loss and comfort problems
* Inferior duct selection = capacity loss and comfort problems
In short, duct design and execution is nothing to take lightly, in spite of how often that very thing is done. "Oh, just throw some flex duct here or chase a length of hard pipe there...you'll be fine!" Would be nice if it worked that way in reality, but I've been around too many botched duct designs and installations to know differently.
Good duct design is just as much good engineering as it is good installation of an engineered design. What I really was getting at in my prior posts is that if you're building a brand new house, concentrate on making that house gain or lose heat SLOWLY. That way we don't have to throw tremendous amounts of energy into the space to keep it comfortable. Meaning your duct design intensity and HVAC BTU requirement decreases. Energy consumption decreases. Comfort year round increases. As an architect designing his or her own house, these aspects should rate high on your "must have" list.