Page 41 - Energize May 2021

TECHNICAL

GEBs have a mix of energy efficiency measures, energy storage, coincides with the solar PV peak. In winter, the main HVAC load will
and energy generation in the form of rooftop PV (typically), and be heating, which will be higher at the early and late hours of the
importantly, a range of flexible loads controlled by on-premises day and decrease around midday. Lighting requirement decreases
computing. This approach results in a lower and often more as natural light increases, and in a modern building would be lower
level energy load profile, which in turn delivers a more resilient at midday.
and profitable building which has access to new revenue Despite this, all buildings exhibit a load which peaks at around
streams as well. 1 midday and decreases substantially outside of working hours.
The nighttime load of a building without efficiency or flexible loads
Load profiles would consist of security systems, common area lighting, computer
One of the aims of the GEB is to reduce the variations in demand by servers and other IT equipment. This contrasts with grid demand,
balancing demand and load in a dynamic fashion. which peaks in the early evening. Some businesses require desktop
• Figure 2(a) shows the load profile of a typical building without computers to remain switched on overnight to allow backups and
energy efficiency measures. The load starts low in the morning software upgrades, which could add a significant nighttime load to
and rises to a sharp peak at noon, dropping to a low value at the the building. Actual measured profiles show a morning peak around
end of the day. 10h00 with a slight drop around 12h00, followed by a second
• Figure 2(b) shows the load profile of the same building where peak around 14h00. This could coincide with lower use of office
energy efficiency measures have been applied. There is a equipment during the lunch break and lower building occupation.
general lowering of the demand curve over the whole day, but
with same sharp peak at midday. Building demand flexibility
• Figure 2(c) shows the profile of the same building with on-site Demand flexibility can be achieved using a combination of smart,
solar PV generation. The profile shows a large dip around noon. flexible loads with thermal and electrical energy storage. A flexible
The extent of the dip will depend on the amount of PV installed. load is one which can be reduced or shifted in time to assist with
In all the above there is a large variation in demand over the day, load-matching and grid interaction to smooth out the demand
and the aim of GEB is to reduce this variation as far as possible. curve. In a non-industrial building, the main loads would be:
• Figure 2(d) shows the demand curve of an idealised GEB, • Lighting: The lighting load would decrease as the amount of
where the variations in the demand curve have been reduced sunlight increased.
considerably. • HVAC: Space cooling or heating, ventilation, water heating
depending on the season.
Commercial building load profiles • Machinery: IT, elevators and other business machinery would
The load profile of a real building varies with the seasons, and this remain generally constant, but may vary in the morning and late
makes a flexible system more necessary. In summer, the main HVAC afternoon as employees arrive and leave.
load will be cooling, with the demand peaking around midday, which • Electric vehicles: EV charging (a new sector which has not been
implemented generally in South Africa, but which could provide
a new profile in future).

Building flexibility modes
There are four modes with which buildings can provide demand
flexibility (see Figure 4).
• Efficiency: The ongoing reduction in energy use while providing
the same or improved level of building function. Most buildings
today have implemented some form of energy efficiency. Energy
efficiency is achieved by modern lighting and lighting control
systems, as well as improved efficiency HVAC systems.
Figure: 2 Load profiles of typical commercial buildings (Rocky Mountain Institute)
• Load shedding: The ability to reduce electricity use for a short
time period and typically on short notice. Shedding is typically
applied during peak demand periods and during emergencies.
Load shedding cannot generally be applied to commercial
buildings without affecting business operations or occupant
comfort, but there are means to reduce loads without
affecting either.
• Load shifting: This is the ability to change the timing of
electricity use to minimise demand during peak periods or to
take advantage of the cheapest electricity prices. A shift may
lead to using more electricity during the cheapest time period
and using thermal or battery storage at another time period
when electricity prices are higher.
• Modulation: This is the ability to balance power supply and
demand or reactive power draw and supply autonomously
(within seconds to sub-seconds) in response to a signal from the
Figure 3: Sample of a commercial building’s load profile (Iowa utilities board). grid operator during the dispatch period.

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