"Correct" mold prevention - attic AC only ducts

[JNXMN]

I know you didnt mean that. But winter mold from sweating inside the ducts is the problem the original poster asked about, and I was just messing with you.

Also, I have a three row coil in my ac and it keeps the house nice and dry. How cold you get the air determines how much moisture is removed, not how many rows of coils.

Hi I agree. What I meant is a deeper coil give you better contact hence better for dehum. When you have a look the coil in an operating theater AHU you'll normally find it comes with 6 rows coil. Of course its with chilled water as well to bring down the off coil conditions n better dehum. (This is based on a hotter n more humid climate.) At the end of the day its depend on how much latent the coil need to meet. A residential situation its probably not that much of a problem if you r not talking a massive amounts of fresh air/moisture. Of course you still need to insulate your ductwork properly to lag the heat transfer n minimise chances of condensation. Sorry off topic a bit.

[JNXMN]

I know you didnt mean that. But winter mold from sweating inside the ducts is the problem the original poster asked about, and I was just messing with you.

Also, I have a three row coil in my ac and it keeps the house nice and dry. How cold you get the air determines how much moisture is removed, not how many rows of coils.

Hi I agree. What I meant is a deeper coil give you better contact hence better for dehum. When you have a look the coil in an operating theater AHU you'll normally find it comes with 6 rows coil. Of course its with chilled water as well to bring down the off coil conditions n better dehum. (This is based on a hotter n more humid climate.) At the end of the day its depend on how much latent the coil need to meet. A residential situation its probably not that much of a problem if you r not talking a massive amounts of fresh air/moisture. Of course you still need to insulate your ductwork properly to lag the heat transfer n minimise chances of condensation. Sorry off topic a bit.

[teddy bear]

if you planning to utilise the AC to dehumidify your house as well. you'll need to oversize your AC in order to draw out the moisture from the supply air. then as other has said, you'll have a re-heat element to bring up the supply air temperature to the set point. all of this cost, both in equipment and operation. also, the general ducted AC DX split system only come with 3 row coils. this is the other question you need to make sure whether the coil has the capacity to handle the require latent load. normally 3 row coils cannot deal with too much humidity. in fact, it's not really designed to take out humidity in air. you will need to be aware of that a normal DX AC system is only designed and controlled by temperature, not by humidity.
your ductwork in attic space will need to be insulated, as much as you can. you want to have non-perforated insulation blanket with sisalation. putting in a small attic ventilation system to generate some air movement will definitely help as well.

"Over sized ac to dehumidify " is not a good strategy. Reheat is not allowed in most energy codes. Air movement in the attic to help duct sweating??
Removing moisture is about cold coils and the length of the cooling cycle. You need a 45^F coil with a hour run time. The drain pan must drain well.
Sorry for being so blunt.
Regards TB

[JNXMN]

"Over sized ac to dehumidify " is not a good strategy. Reheat is not allowed in most energy codes. Air movement in the attic to help duct sweating??
Removing moisture is about cold coils and the length of the cooling cycle. You need a 45^F coil with a hour run time. The drain pan must drain well.
Sorry for being so blunt.
Regards TB

Absolutely right. I think I need to make it clear. I'm against oversizing equipment and add reheat. I also think its not much of problem in winter as long as insulation is properly done. I'm just saying a normal DX split does not give you the ability to actively control humidity. It only gives you temperature control. Venting the attic space will help in summer.
The latent capacity of the unit/coil provide you the dehum.

[JNXMN]

"Over sized ac to dehumidify " is not a good strategy. Reheat is not allowed in most energy codes. Air movement in the attic to help duct sweating??
Removing moisture is about cold coils and the length of the cooling cycle. You need a 45^F coil with a hour run time. The drain pan must drain well.
Sorry for being so blunt.
Regards TB

Absolutely right. I think I need to make it clear. I'm against oversizing equipment and add reheat. I also think its not much of problem in winter as long as insulation is properly done. I'm just saying a normal DX split does not give you the ability to actively control humidity. It only gives you temperature control. Venting the attic space will help in summer.
The latent capacity of the unit/coil provide you the dehum.

[JNXMN]

Absolutely right. I think I need to make it clear. I'm against oversizing equipment and add reheat. I also think its not much of problem in winter as long as insulation is properly done. I'm just saying a normal DX split does not give you the ability to actively control humidity. It only gives you temperature control. Venting the attic space will help in summer.
The latent capacity of the unit/coil provide you the dehum.

I must also clear my statement that cooling coil will of course remove moisture . Just not controllable. As long as you don't need to fix yr RH level within a certain range. You don't need reheat.

[JNXMN]

Absolutely right. I think I need to make it clear. I'm against oversizing equipment and add reheat. I also think its not much of problem in winter as long as insulation is properly done. I'm just saying a normal DX split does not give you the ability to actively control humidity. It only gives you temperature control. Venting the attic space will help in summer.
The latent capacity of the unit/coil provide you the dehum.

Or you might want to bolt a dehum unit at the return terminal for humidity control if it is necessary.