Carrier/Bryant, Infinity/Evolution Zoned system Indoor Coil Size help
I am new to this forum and seeking some sound technical advice on a new HVAC system.
I have had numerous HVAC contractors review my home in the Chicagoland area and have found that most of them used rules of thumb rather than actually doing the calculations which made me quite nervous. I want a full zone system which is going to be very expensive to have installed so naturally I want to make sure it is done right.
I have been unable to find a contractor who is knowledgeable enough to answer my questions with enough technical details and have since spent the last couple of months researching and learning the details on my own.
I have probably spent entirely way too much time researching and reading all of the product data, my wife thinks I am crazy…but actually I am finding it very interesting and even kind of fun.
I have decided to go with the Carrier/Infinity/Bryant/Evolution zoning system as I can see the many benefits it brings with the communicating system adjustable CFM, and it seems to really handle zoning nicely. Most of my knowledge comes from the internet and reading all of the product data manuals for all of the components.
To do this system the correct way every bit of ductwork needs to be torn out in my basement and redone to be much larger in size to keep the velocities and static pressures down. I need to have additional supply ducts added to a couple of rooms that are always too hot in the summer and quite a few additional return ducts throughout the house also. I was very surprised when I found out how much all of this will cost me but I am now convinced that it will be worth it in the end.
My current plan is to go with Carrier or Bryant. The Bryant Furnace - 355CAV060-100 (100KBTU, 3 stage with variable blower) same as Carrier 58MVC100-120 and the Bryant 187B-NA048 4-ton A/C,(2 stage Puron ac unit with the low stage of about 60% or 2.4 tons), same as Carrier 24APA7-48.
I feel comfortable with my top pick contractor in his revised duct design as well as his choices and sizing of the furnace and outdoor condenser however the biggest question that I cannot seem to get resolved is what size indoor evaporator coil should be used. A 4 ton to match the condenser or upsize to 5 ton for a little better efficiency, higher BTU and a slightly lower pressure drop through the coil. I was able to find the 3 Carrier coils in question on the AHRI website as matched with this furnace and outdoor unit and found the SEER ratings etc. I have also learned however that a higher SEER rating isn’t necessarily the best thing to do especially for humidity removal.
I want to make sure I have enough latent capacity to remove humidity in my geographical location. Is humidity in Chicago considered average, high or low? I also know that the Infinity control has a feature that will reduce the CFM of the blower to help lower the coil temperature and remove humidity (increase latent capacity) if necessary so I may not have a problem but I still want to understand the logic and make sure the coil I get is the best choice.
The AHRI data is as follows for the 3 coils matched with the above furnace and outdoor condenser:
4 ton coil (same 21” width as the furnace)
• Capacity - 47,500 btuh
• EER - 12.3
• SEER - 15.5
• Coil pressure drops are the highest with this coil, around 0.02 w.c.
more at low CFM and about 0.08 w.c. more at the higher CFM (may be nothing but it sounds like a lot to me) Does it matter?
4 ton coil (3" wider than furnace, I was told that wider was ok and didn’t matter, does it?)
• Capacity - 47,000 btuh
• EER - 12.2
• SEER – 16.2
• Coil pressure drops are lower than the other 4 ton coil
• I don’t understand. How can the btuh rating of this coil be lower yet the SEER rating is higher? That doesn’t add up to me.
5-ton coil (3" wider than Furnace)
• Capacity - 48,500 btuh
• EER - 12.6
• SEER - 16
• Coil pressure drops are just slightly lower than the 4-ton coil above
• This coil had the highest btuh capacity
There is also another 5-ton coil which has even higher btuh and SEER ratings but it is too tall and the ceiling in my basement is too low.
All coils come with a TXV which is good but the 5 ton coil comes with a different TXV than the 4 ton coils. I assume the 5 ton TXV has a higher capacity but I am not sure if this is a problem when matching with a 4 ton condenser, any thoughts on that? Also what happens when only the low stage of the outdoor unit (2 stage compressor) is running at about 2.5 tons, will the large 5-ton coil and 5-ton TXV cause problems? The blower CFM is also reduced when running in low stage but I wonder if a large coil is actually less efficient at low speed.
With the zoned system it is likely that the unit will run at the low 2.5 ton stage the majority of the time and only kick into 4-ton mode when all zones are calling for cooling. I would think that the low stage plays a major factor in the coil selection especially when zoning.
I have had contractors tell me that the 5-ton coil is best and others that are convinced that the either one of the 4-ton coils is better and neither one have any data or logical explanation to support either one.
Could someone please help? I may be over thinking this whole thing but I just want to make sure it gets done right and now my curiosity really makes me want to understand WHY and learn how it works.
THANK YOU IN ADVANCE FOR ANYONE THAT CAN HELP!
Consumer Reports and the US Dept. of Energy recommends the you do not use any contractor that does not run a heat load. I would insist on a "Right Size" guarantee and a 12 month "Buy Back" guarantee. Then any contractor worth a darn will invest the time to do it right.
Bryant dealers all over America are offering these guarantees. BTW I think the Infinity/Evolution equipment with Bryant/Carrier zone control is excellent! But the installing contractor is what you MUST be concerned about.
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Personally I recommend going with a 4 ton coil that is designed to match the seer rating of your 4 ton outdoor unit. If you are going for tax credit and both the 4 ton coils you listed meet the AHRI rating and give a number to prove it, then a lower pressure drop accross the coil is better. Some don't like the coil cabinet to look wider than the furnace, but actually 3" is only an 1 1/2" on both sides and the drain pan in the cabinet will account for that and means no loss of coil surface. The lower pressure drop can account for the higher seer rating as well.
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