New Mexico, Converting From Evaporative Home cooling to AC?

[Tim Fastle]

We have a 3600 sf home with an attached 700 sf Casita (or guest house) that has radiant floor and baseboard heating (so no air handler) and evaporative cooling. We are considering converting the cooling to AC and would like to see if anyone has any input into IF we should do it and HOW it might be best done.

Currently there are two MasterCool evap units on the main house and a smaller Champion evap on the Casita. The MasterCool units are down draft and each one goes into independent venting systems (1 is basically the living areas, the other is basically the 3 bedrooms). The cooling units are on a flat roof (adobe style home) and, although they are only about 15' apart, the venting systems are not connected. The Casita cooler has it's own minimal venting system.

We grew up in Albuquerque and 6 years ago moved back. I know when I was young evaporative cooling was the most common system because of cost and effectiveness. I believe now that refrigerant systems have gotten much better and more efficient and, it seems, are a superior option even in this very dry climate. Does that sound correct? It sure seems like the homes and businesses I go into that have refrigeration AC cool much better than the swamp cooler homes and businesses do.

I have called around to some HVAC professionals and it seems that each wants to do it the way that they want to do it and I am not sure if that would be the "best" way to do it so I thought I might get some input from the brighter and more experienced minds that are on this forum. It seems to me that an ideal way to handle it would be a single compressor/condenser coil unit tied to 3 air handler/evaporative coil units, one handler each located where the old evaporative coolers were (of course, each one sized for it's task). I know very little about such a conversion and don't even know if what I described above is possible. Is it and would it be the most cost effective way to design such a system? Or, would there have to be a combination AC unit/Air handler for each venting system (3) and might that even be the most cost effective way to design the system? Or is there a better way to go about it? Or, are we better of just sticking with the evaporative coolers?

My experience is that as you begin to consider something like this it's best to have an idea of what your best options might be so, as you speak to the "experts", you don't end up with what is best for them and maybe not so much for you. Any thoughts, ideas or input would be greatly appreciated! If I left something out or there are questions, please ask away.

Thanks in advance.

 

[Fitter30]

There are several different ways to go from muilti head mini splits to using a package unit mounted on the roofs with exposed spiral duct all depends on costs. Need a company that will run a heat load on both building using manual j program. Contact your electric company see if they do a energy audit with a blower door test ( tell how tite the buildings are) and with them for rebates. Brand of the equipment is secondary to to contractor installation. The higher the seer rating the more experienced tech will be needed.

 

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[Tim Fastle]

Thanks for the reply fitter. So are you saying that there are really only two options - either a Mini Split system or mulitiple Package Units mounted on the roof and there is no such thing or option of a system with one large compressor unit feeding multiple air handler/evaporator coil units mounted on the roof? Also, you mentioned using exposed spiral ducts. Would that be in addition to (or in place of) the ducting system my house already has for the evaporative units? And why would I need the additional ducts?

Thanks!

 

[Fitter30]

Not knowing how swamp cooler duct is designed and no return air spiral duct might give you another option. Any system with a separate condenser have a line length maximum didn't know if the casita was attached.

 

[Dana]

Like anything else in HVAC, to find the optimal solution starts with a room by room, zone by zone Manual-J load calculation. Try CoolCalc (dot com) or LoadCalc (dot net), and be aggressive rather than conservative- oversizing by more than 1.2x cuts in to comfort, more than 1.5x starts to cut into efficiency.

Odds are pretty good that there is a high 2-3 ton SEER 3 zone modulating heat pump solution for you that could also serve as auxiliary heat when desired/cheaper/necessary, probably using the same ducts. Any AC or heat pump has to be correctly derated for altitude- the capacities start to drop significantly when above 5000'. Sometimes (often, really) it's cheaper (and almost always better) to use 3 separate compressors when using modulating equipment. There are DIY-able ducted mini-splits out there with decent SEER & capacity specs that could work quite well on a variety of existing ducted systems. (Carrier has been putting their label on good-to-excellent inexpensive Midea units for more than a decade now, both slim-ducted & ductless.)

In locations as dry as NM it's fine to go with ultra-high SEER 25+ equipment since the latent loads are largely negative. In the sticky gulf coast states AC with SEER numbers that high doesn't remove enough moisture out of the air, and often needs a whole house dehumidifier to find true comfort. Midea/Carrier has a few 3/4 ton & 1-ton ductless mini-splits in the SEER 40+ range (eg- this one) that might be a good call for zones with wide open floor plans.

Almost all DIY ductless minisplits out there are re-labeled pretty good Mideas (Mr. Cool, Pioneer, Senville, Blueridge et al), some of which are in the mid to high 30s for SEER rating.

Do you have the CFM specs for your swamp coolers? (That would give at least some idea as to what to expect for ducts.)