Amana is a Goodman brand... in the larger sizes Goodman is the most economical choice... for a commercial building I would go with Goodman equipment, it will cost less than anything else on the market by a wide margin, it uses off the shelf parts... and is easy to service.
If you want to spend about 30% more get a quote from a Carrier dealer, or a Trane Dealer.
A system large enough for 4.500 sq feet requires some applications engineering, I can submit an additional services offer for that, or, you can ask for bids from the local contractors.. they will include the applications engineering in their estimates.
Tell them that you want the 'builders model' in equipment. A building that size in your area will require about 10 tons of cooling capacity if it does not have a lot of south and west facing unshaded glass. (120,000 btu's per hour)....get offers on two 5 ton systems, and on one 10 ton system.
Deal with the best established and lowest priced HVAC contractor in the area.
That sort of equipment will be the most rugged, lowest cost, equipment on the market.
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