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Shell vs. Load Dominated Buildings

By April 12, 2012December 26th, 2021Briefs

Setting the Scene

Imagine yourself as a prep-cook in a small but well lit kitchen before the big lunch rush. You and three others are bustling about, chopping veggies, pulling things in and out of hot ovens, hacking chunks of meat, jostling hot pans of sweet potatoes as fryer grease droplets reach out to touch you, and hot blasts of steam…stop! If you were to say that this is a high energy environment, you would be correct. For sure in terms of energy and heat transfer!

All of the people, equipment and lights in the space are producing heat. In our industry we call these heat sources internal loads. A large percentage (if not vented outside via an exhaust hood) of these internal loads is transferred directly to the space which is why it literally starts to heat up, but it doesn’t take just hot cooking equipment. Office and other electronic equipment can do plenty of heating as well. The heat cannot escape fast enough through the walls and it doesn’t seem to matter if its summer or winter; fancy that. A building with this phenomena occurring is called internally load dominated or just load dominated. Many multistory retail and office buildings are generally load dominated as well.

Now imagine that you are all alone in a garden shed in Wisconsin. Here, as you sit inside and contemplate life, you probably can’t get comfortable at all: way too hot in July and freezing in January. There maybe a few months in the spring and fall that would be agreeable, but it can be said that the outside weather conditions dictate what sort of loads the shed is experiencing. And what is between you and the load presented by the weather conditions outside? That would be the shell (also called the building envelope) of the shed. From an energy perspective, we would call this a shell dominated building. One-story commercial buildings without a lot of internal heat, warehouses, and single family homes are considered shell dominated buildings.

Why is this Important?

These were two very different examples but they illustrate an important design concept that is often overlooked or at least misunderstood by some designers and the general public. Many people talk about how super insulation is key for energy efficiency. Super-insulation is certainly not the answer for most commercial buildings. In fact, too much insulation can keep too much heat inside of a building running the air conditioning all year round, even in northern climates!

I recently worked on a LEED® whole building energy simulation for an office/retail building which had typical office internal loads but major additional insulation. The cooling energy increased as a result and the air conditioning ran well through the winter months. This occurs during unoccupied hours when less heat can escape while the building is shut down, but it may not be cool and dry enough outside to take advantage of free cooling (economizer). Increased insulation levels would normally benefit a shell dominated building up to a certain point. Perhaps a more important consideration than insulation in commercial buildings is the thermal mass within a building and its effects on loading.

Michaels Energy

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