Upstairs, there are three bedrooms, bathroom and a landing area at the top of the stairs. At the top of the landing area there are 2 bedrooms to the right and one bedroom and one bathroom to the left. Straight ahead at the top of the stairs is a doorway which leads directly into attic one and where the air handlers are located. Total living area upstairs is 700 sq. feet
Next problem is that the original outside units were squished together. In order to space them far enough apart from each other ..24 inches (just barely have room) we have to place one of the compressors over our buried utilities...sewer, phone and electrical service....aaaargh Is this something that should also be a concern?
I have been researching for my own home the type system shophound has referred to as the multi-split system. There are a lot of positive features of these systems. Look at manufacturers such as Daikin, Sanyo and Mitsubishi.
One issue is the size of the single outdoor unit that is capable of having multiple indoor units connected to it. The outdoor unit from Daikin has a foot print of about 36 x 14. This would resolve your outdoor space issue. Additionally, they are normally much quieter when running.
These systems are inverter driven and are virtually the only types of systems installed in most other countries. Inverted means the AC current we have in our homes is converted to DC current which allows for the motors (compressors and fans) to be varied in speed of operation and thus variable in capacity. System capacity can often go as low as 30% of nominal capacity. The one outdoor unit can operate multiple indoor units as they call for cooling or heating by varying the output to meet the demand. Additionally, because of the varying capacity they are generally more efficient then the typical type system we find here. Being as you are so far south it would not surprise me if you would be able to fully heat your home with the heat pump without any back up heat needed. The Daikin 4 ton model produces about 44K Btus at 22*. Sanyo has one that produces about 52K at that temp. In comparison, a high efficiency Carrier heat pump puts out about 31k at that temp at a lower COP (2.91 for Carrier vs 3.14 for Daikin).
The outdoor units can also go as high as 130% of nominal in cooling mode so you may be able to use a 3 ton model. The Daikin unit produces 38K cooling at 95* outdoor, 67* wet bulb indoor.
The air handlers are configured a little differently than what we are used to, but I would think it would not be difficult to retrofit them to an existing duct system.
Hope this is helpful.
I believe to keep things simple, you probably should shelve what I said about oversizing and rely more on what Shophound said. It certainly is true you want to keep good dehumidification ability no matter what. I think there are some interesting angles to discuss but another time and place would be better.
You certainly can find mini-split ACs which have 3 indoor units for the 3 bedrooms, all fed by one outside unit. One example:
That outside unit could be mounted on the outside wall, which sounds to me like a solution to your existing 2 outside units mounted too close together. I understand these "inverter" systems are variable capacity so this changes the judgement on oversizing. Find a credible pro (likely from this board) and check with him.
If there is a real scarcity of local talent, if in your shoes I would want to consult with a real expert and have him build specs for what the local hands-on guy would do. This is not a common way of doing business, but then again the usual way often leaves something to be desired.
Best of luck -- Pstu
Originally Posted by pstu
Please let me clarify that what I suggested with respect to investigating multi-split systems is different than the mini-split system pstu is referring to here.
The Daikin multi-split system, as an example, is designed to work with ductless and ducted air handlers that can be used with your existing duct work. They have nine air handlers that you can match up to the outdoor unit that range from 1 ton to 4 ton (cooling) and can be fitted to duct work with various different external static pressure. Obviously, making changes/improvements to the duct work is highly important to getting an optimum system. This would include checking the sizing and air flow capabilities, ESP, along with sealing and insulating.
The mini-split systems are ductless but have a self contained coil and blower to be placed within the living areas to be conditioned. They typically get set flush into the ceiling or are wall mounted. This is another option too.
It's Not Rocket Science, But It is SCIENCE
with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
Don't go by what "tons" are on Man J look at sensible and latent load- then look at the expanded ratings of the equipment selected for the conditions in your area