[Greenbuilding] One more question on AC

[John Straube]

A massive benefit of mini-splits is their ability to reduce their output by a factor of about 4 to avoid short cycling.  Unless you insanely oversize, this works, based on first hand experience with a lot of installs going back years.
The two stage systems from Carrier Trane etc are not as good at this but way way better and for many applications, they work very well, reducing over sizing short cycling from a common problem to a rare problem.  
 The Carrier 2 stage 2 ton system still cools at 13 kBtu according to the Carrier technical manual I have (for the 25 VNA), and I think Alan may have made a mis-type.  Would be news to me that Carrier makes anything that modulates that low!!

On 2013-07-09, at 5:45 PM, John Salmen <terrain at shaw.ca>
 wrote:

> Used to have a concern with oversized pumps cycling inefficiently. Don’t know if that is still a concern with ‘newer’ tech
>  
> From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Alan Abrams
> Sent: July-09-13 2:32 PM
> To: Green Building
> Subject: Re: [Greenbuilding] One more question on AC
>  
> 
>  
> the heating and air will be an inline Fujitsu, about 18KBtu capacity.  It's oversized for the calculated loads, but only to push enough volume to handle dehumidification and prevent hot spots.  One concern is overheating in shoulder months, when the leaf cover is gone and the sun is lower than the overhangs--which are tuned for summer shading and max winter gain--IOW's we anticipate days where some cooling may be required in the afternoon, and heating is required later at night.  
>  
> at a ton and a half, it raises the question of why not just go with a 2 ton Carrier Infinity, with almost twice the fan capacity--but still able to wind down to maybe 3KBtu.  But we decided to do a fine tuned duct system, reducing the trunk at each tap, with sweeping takeoffs and boots, to reduce friction where-ever possible.
> 

John F Straube
jfstraube at uwaterloo.ca
www.JohnStraube.com