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Thread: New house! Eternal heater w/ solar preheat?

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  1. #16
    In the trades Dana's Avatar
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    Jan 2009


    Quote Originally Posted by Steve29 View Post
    Excellent summary of singles vs a multi - thanks! I didn't realize the 3" lines were carrying refrigerant. I'll look into wall vs ceiling mounts and continue on the Taco expedition (am a little nervous of what it'll tell us....)
    The Taco heat loss tool will just tell you what you already know, but it'll put a number on it. Having a lot of glass is pretty lossy (gain-ey, if in direct sun). Finding the right balance between the aesthetics, thermal performance, and costs (capital & operating) is never simple- it's an iterative process. Cutting the glazed area 20% is usually far cheaper than increasing it's performance 20% with extra coatings, exotic gases, & extra layers. It's sometimes possible to cut the losses elsewhere with high-R wall & roof assemblies, but costing that out is also not simple.

    The last thing you'd want to do is keep the field of view large, but end up cutting out so much of the light with the high-performance windows that the view looks dull and it's so dark you need to turn on the lights to read your watch, as sometimes happens with some of the more serious heat-rejecting goods. The view out of a 15' x 8' wall of glass isn't much compromised by reducing it to 14' x 7', replacing that ~18% of U0.33 glass with R20+ (sub U0.05) wall is a 17%+ cut in total heat loss out of that wall. Then bumping the windows from U0.33-0.34 down to U0.29-0.030 buys you another ~10%, usually without breaking the bank or ruining the daylighting or view. Adjusting the size & shape of the windows to optimize the view using the minimum of total area counts for a lot- make the case for every square foot.

    The conduits housing the insulated refrigerant lines DO look a lot like high-velocity mini-ducts, but "ductless" is a key factor in the high efficiency of ductless systems. Without ducts there's no duct leakage losses or backpressure increasing loads to the air handler. If you literally never clean the filters on the interior units of split system it'll cut into efficiency measurably, but not as much as going to a ducted system. Using indoor units with continuously-variable speed blowers rather than some of the simpler 2-speed also improves average efficiency.

    The ceiling mount units tend to look like this:

    But there are flush-mounted versions too:

    Most of the ceiling mounted units are well north of 10,000BTU- finding one appropriately sized for a bedroom might take a few discussions with distributors or manufacturer's reps, since they're usually targeted at larger commercial installations that have far more ceiling than wall as opposed to single-office/room type installations.
    Last edited by Dana; 09-09-2011 at 02:55 PM.

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