Civil Engineering Reference
In-Depth Information
12.7
Sum-Zero Energy Buildings
The concept of Sum-Zero Energy Building (SZEB) has been looked at from differ-
ent point of views and has defi ned with dissimilar targets in different literatures.
For example when the target of the building energy consumption evaluation is to
provide enough renewable energy on the project site to offset all the site's yearly
demand, it is referred to as the whole building site energy consumption, but when
the target of the evaluation is to include enough renewable energy on the project site
to offset the total energy used for generation and delivery of the yearly energy
demand of the building including its site to the site, it is known as the source energy
consumption. A SZEB also have been referred to a building that the cost of the
energy for the owner is at least equal to the money that the energy grid provider pays
to the building owner for the amount of the energy that his building delivers to the
grid. Finally in some literatures an SZEB has been defi ned as a building that pro-
duces at least enough emission-free renewable energy to cover the emission gener-
ated by its non-renewable energy sources.
Before going any further, let's discuss the difference between the source and site
energy with a little more detail. As it was said earlier, site energy is basically the
amount of the energy that has been brought to the site and the source energy is the
total energy used to produce and transfer the energy to the site. Since each region
has a different structure for energy delivery and also uses different resources and
also equipment to generate electricity (as an example), therefore the conversions
used for calculating the proper multipliers for source energy calculation is different
in each region. For simplicity and ease of understanding let's assume the only source
of energy which is used in a building is electricity and the annual energy consump-
tion of the building is 100,000 kW h. The site energy can be calculated by simply
converting this 100,000 kW h to its equivalent in terms of kBtu. No matter where in
the country this building is located, we can use this conversion to calculate its site
energy (e.g. the site energy for this building will be equal to 100,000 kW h × 3.413 kBtu/
kW h or 341,300 kBtu).
Now assume this building is located in a region with a Source Energy Factor
(SEF) of 8.05. (The electricity source energy factor is defi ned as heat input in
MMBtu/net generation in MWh, and as it was said earlier is different from one
region to another due to their different structure for energy delivery and also use of
different resources and equipment to generate the targeted energy type.) Therefore
if this building still consumes 100,000 kW h electricity per year, then its source
energy will be calculated by multiplying the electricity consumption by the source
energy factor for that region. That will results in 100,000 kW h × 8.05 kBtu/kW h or
805,000 kBtu. If this building was located in another region with source energy fac-
tor of 6.08, then its source energy could be calculated as 100,000 kW h × 6.08 kBtu/
kW h or 608,000 kBtu.
Implementing each of the discussed strategies in defi ning the concept of SZEB
and therefore calculating the total energy consumption of the building based on that
specifi c defi nition obviously has its own positive and negative associated issues.
