I’ve spent the majority of this week in barns doing ventilation (and feeder/drinker) reviews of both new construction, 1-2 year old facilities and 40 year old facilities. It’s amazing to me that the same common mistakes keep showing up. While we think we know better how to design, install and manage ventilation system components, the screw-ups remain the same.
A major mistake that I saw repeatedly this week was incorrect sizing of attic inlets (generally soffits). You can’t get air out of a barn if your fans have to work too hard to get air into the barn! While I haven’t worked the numbers from the site visits yet, at one facility I’m pretty sure that when the last fan stage came on static pressure increased enough that the total cfm of air exhausted went down while the electric bill went up because there wasn’t enough attic inlet opening!
On the other hand, I saw some facilities with awesome attic inlet openings. One builder in South Dakota doesn’t use soffits for the attic inlet – they see too many soffits plugged and/or abused among their clients. They have gone to using the east and west gable ends as inlets for curtain barns oriented east-west and the conditions in the barns as a result were excellent!
I was asked by a builder last fall if you could make an attic opening too big – NO! If you have fewer (or no) restrictions before air gets to the ceiling inlets the fans only have to work with the restrictions you place at the inlets and at any pit fans on pit lids or plenums. In addition, if you have counter-weighted inlets, the more the attic is the less likely strong southerly winds will push the inlets open, a common complaint for those of you with weighted inlets.
I continue to see fans and inlets not correctly matched for size (capacity), especially in remodeled facilities. If you have too much inlet capacity relative to fan capacity, it is really tough to get the inlets adjusted tight enough for stage 1 and 2 ventilation. If inlets are too small relative to fan capacity, fans work hard and don’t move the air you intend while consuming more electricity.
Ventilation occurs when you design and manage all components of the system correctly. Wet pens, high fuel bills, high electric bills, etc. occur when you make a mistake in any of the component design or management details.