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Old 07-14-2014, 12:58 AM   #1
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What kind of HVAC might be on this homes roof?


See photos. The house is in my neighborhood. I can only see the from the side walking by the house. But able to see a bit from the top of the roof via Google Maps.

This looks like a visible duct on roof running from one part of house ducting back to another part like a tunnel. I've never seen this kind of setup on a residential property.
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Old 07-14-2014, 06:14 AM   #2
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What kind of HVAC might be on this homes roof?


The type where you're not sure if you need to call a roofer or a HVAC tech to fix that terrible DIY job.

I don't know why, but I kind of suspect meth lab ventillation.

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Old 07-14-2014, 09:04 AM   #3
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What kind of HVAC might be on this homes roof?


Basic packaged AC unit you see on strip malls. 7-Elevens etc all the time. Because it has a flat / low slope roof. The long snaky pipe is the central return air pipe probably. Can also see the black grill over the condensor fan.
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Old 07-14-2014, 10:31 AM   #4
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What kind of HVAC might be on this homes roof?


Go to Phoenix, or come to Vegas and you will see that is quite common on some older houses with little to no attic space. Sometimes when people add an addition to the house it is the only way to get air to the new area.
The only way to do that properly, if you can call it proper, is to run insulated flex duct through the round pipe.
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Old 07-14-2014, 12:44 PM   #5
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What kind of HVAC might be on this homes roof?


do they make small chillers for situations like this?

i imagine a couple of 1" insulated pex pipes with like 45 degree water could carry away a substantial amount of heat.

the space advantages are obvious, with respect to the pex. How large are fan coils etc, tho? those could surely be installed... more or less, as a mini split evaporator is.

edit: grammar

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Old 07-14-2014, 01:54 PM   #6
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What kind of HVAC might be on this homes roof?


No. Chillers are very expensive to produce and unfortunately they don't get you a 34-36 deg F coil like a regular AC will and don't de humidify as well.
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Old 07-14-2014, 04:21 PM   #7
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What kind of HVAC might be on this homes roof?


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No. Chillers are very expensive to produce and unfortunately they don't get you a 34-36 deg F coil like a regular AC will and don't de humidify as well.
excellent point regarding the humidity.

are chillers necessarily more expense tho? i mean from a material standpoint, not an economic one.
from what ive seen in my hvac books, they just require more instrumentation, and a different evaporator obviously.

don't they make plate heat exchangers that can handle r 410 pressures?
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Old 07-14-2014, 04:33 PM   #8
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What kind of HVAC might be on this homes roof?


I would figure if the house has no existing ductwork a few mini splits would make more sense.

All that ducting through the outside walls/roof can't be great for the R value and vapor barrier value either.
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Old 07-14-2014, 05:25 PM   #9
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What kind of HVAC might be on this homes roof?


Quote:
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excellent point regarding the humidity.

are chillers necessarily more expense tho? i mean from a material standpoint, not an economic one.
from what ive seen in my hvac books, they just require more instrumentation, and a different evaporator obviously.

don't they make plate heat exchangers that can handle r 410 pressures?

Chiller is a generic name. Basically they chill water which is used in a cooling coil and they can cool glycol also. They vary in size from 20 ton as the smallest to 4000 tons (Trane) or more with absorption chillers in Lumber mills and huge industrial plants. There are screw compressor type and huge centrifugal and absorption chillers. Google Trane/Carrier/York/McQuay chillers for more info. I worked with 250/500 and 1000 ton centrifugal and screw type chillers and some with vfd variable frequency drives. Huge industry and a whole different business when you get into the really big stuff.

They are physically big and heavy. There are smaller reciprocating semi hermetic chillers but I doubt any are less than 10 tons which is way too big for most houses.

When you get big chillers over 50 tons they are like buying a Caterpillar engine. Cast iron and huge. No demand for anything like that for residential use.

http://www.trane.com/commercial/nort.../chillers.html
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Old 07-14-2014, 05:30 PM   #10
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What kind of HVAC might be on this homes roof?


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Originally Posted by Red Squirrel View Post
I would figure if the house has no existing ductwork a few mini splits would make more sense.

All that ducting through the outside walls/roof can't be great for the R value and vapor barrier value either.

10 yrs ago we had no mini splits in North America or very few. Therefore those homes in Vegas etc would have the roof unit. Or a swamp cooler.

Mini splits are expensive and a huge pain in the butt to install. The logistics of where the indoor unit will fit and drain etc are too much for some jobs. Nothing wrong with a roof unit if it is installed properly. They can have zone dampers and be zoned. Geo thermal is very popular with huge mansions nowadays.
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Old 07-14-2014, 06:32 PM   #11
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What kind of HVAC might be on this homes roof?


Quote:
Originally Posted by yuri View Post
...
They are physically big and heavy. There are smaller reciprocating semi hermetic chillers but I doubt any are less than 10 tons which is way too big for most houses.

When you get big chillers over 50 tons they are like buying a Caterpillar engine. Cast iron and huge. No demand for anything like that for residential use.
yea,i understand what you are saying, the industry norm is for very large scale chillers. i also get that very large chillers require compressors beyond the hermetic units.

But small chillers, could easily use the nice and quiet, hermetic type compressors, and HFC refrigerants, from what i understand at least.
its just that nobody bothers to build them im guessing.
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Old 07-14-2014, 06:50 PM   #12
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What kind of HVAC might be on this homes roof?


I believe Unico makes a reverse cycle chiller in a 3 ton, and 5 ton size. Multi Aqua also makes a 5 ton chiller for their ductless split units.

There are also niche market small capacity chillers.
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Old 07-14-2014, 07:05 PM   #13
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What kind of HVAC might be on this homes roof?


The fact they don't de humidify well is an issue unless you live in a dry climate. We have condos from the mid 70's with a central chiller system for 200 of them. Coil never gets cold enough to de humidify well. Same thing when I worked in a hospital. Getting rid of humidity is the issue. The advantage is the sheer capacity. Running a 1000 ton chiller is fun. With vfd drives you can slow them down and run them in cool weather.
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Old 07-14-2014, 07:28 PM   #14
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What kind of HVAC might be on this homes roof?


Chiller/chilled water systems dehumidify fine. Problem is many large places try to cheap out on operating cost, and run the water/glycol temp too high. Many places let the water temp rise to 55F(12.7C).
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Old 07-14-2014, 10:34 PM   #15
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What kind of HVAC might be on this homes roof?


The real issue with the chiller systems is you have to pump massive amounts of coolant (water) to get any cooling capacity. The dx refrigerant systems absorb most of the heat from the air in the form of latent heat exchange by boiling off the refrigerant in the indoor coil, a chiller system relies on using sensible heat exchange which requires a lot more pounds of coolant to be circulated to get the capacity you need.

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