Thinking bubble wrap in August

The most popular topic for me this summer and fall at producer meetings is managing propane expense in swine facilities. When combined with the supply side concerns, producers have taken on a new awareness of how heating systems work in their facilities and where heat loss is occurring.

The reason I mention this on an August summer day is that today I received notification that the latest issue of the Nebraska Energy Quarterly is available from the Nebraska Energy Office. The link to this issue is:

In this issue is a great discussion of foil-faced bubble wrap. The article basically says foil faced bubble wrap, which many in the upper Midwest install in sidewall and tunnel curtains in winter, only has an R value of about 1.

Yet I hear from many producers about the effectiveness of this product. We use it at SVC Research in our facilities and it does make a difference in pig comfort and winter ventilation.

Why does it work if the R value is so low? I think a big benefit is that the bubble wrap, when installed between the bird netting and curtain, stops all of the air leaks associated with curtains as they age. I know in a lot of facilities that I get into the ceiling inlets work much better in winter with bubble wrap installed in the sidewall curtains.

How many facilities have curtains where producers decide to get ‘1 more year’ out of the curtains before replacing them? How many of you have barns with curtains that are full of pin holes from power washing wands, small wear lines from ropes rubbing, small mouse holes from a summer of never moving the curtain, etc.

All of these add up to leakage. Keep in mind that a facility with 2-24” fans on variable stage 1 operating at 50% cfm only needs 8.5 sqft of total opening to the room to get 800 fpm inlet velocity (this is what what we target in facility management). By the time you add up leaks around doors, shutters on unused fans, curtain pockets, uneven curtain roping and worn curtains, no wonder winter ventilation can be a challenge.

A second benefit of foil faced bubble wrap is radiant heat reflection back to the pig. Pigs in pens with foil backed bubble wrap installed ‘feel’ like the exterior wall is warm because radiant heat from their bodies that is normally lost to a curtain is instead reflected back to the pig.

Finally, there may be an additional increase in installed R value if there is a small trapped air space between the bubble wrap and curtain. However, I don’t count on this when I compute heat loss from a facility since all too often wind pushes the curtain tight to the bubble wrap.

I continue to recommend the installation of bubble wrap in curtain openings in winter because of the reflected radiant heat and tightening of the curtain opening. However, savings in propane expense generally come about because of better ability to manage minimum ventilation rather than a large decrease in heat loss thru the curtain sidewall.

4 thoughts on “Thinking bubble wrap in August

  1. As we continue to fine tune the management of our AirWorks systems, we see less and less propane use. The better the control of the air movement on low ventilation rate days, the less propane.
    Hope you are well!

  2. I agree that controlling the minimum ventilation rate is a key to controlling propane expense. All too often I see minimum ventilation rates increased in response to wet floors when the correct solution is to tighten inlets so incoming air velocity is increased and more mixing of the air occurs. Bubble wrap installed in many curtain walls helps tighten ventilation so minimum has a chance to work correctly.

  3. What about running the fans at full speed, but only half the time? I know you aren’t supposed to, but I’m not sure why. It really helps keep the airspeed up when the curtains are less than perfect.

  4. In some situations we do indeed use fans on timers (x minutes on and x minutes off) and most controllers have this capability for stage 1 fans. The risk is large temperature swings due to the on-off nature of the ventilation. When I’ve been involved in situations with fans on timers, I generally recommend no more than a 3 minute cycle (on plus off time). This minimizes temperature swings. Generally you also have to set the furnace off temperature lower relative to controller set point or the on cycle of the fan will cause enough of a temperature drop to trigger the furnace cycle and then heating costs really get out of control. Timed fans don’t work very well with actuated inlets as this is too much open/close cycling. When you use timed fans, the inlets must shut during the off period of the cycle or warm moist air will backdraft into the attic, especially on windy days when the uplift from ridge vents can be considerable.

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