At Novartis, we use an advanced procedure for benchmarking the energy use of our buildings. We compare the annual, weather corrected energy use of buildings with their respective energy efficiency target. The performance versus target percentage allows perusing improvements over time and serves as a basis for benchmarking buildings in different locations. The total and per area specific energy use of buildings is determined and monitored for key office, laboratory and manufacturing buildings.
To calculate building energy efficiency targets, correction factors and performance data reporting and benchmarking, we have developed an excel data sheet.
How does Novartis determine energy efficiency targets for buildings?
Energy efficiency targets for buildings are specified in terms of energy intensity per floor area, the ratio of annual total energy use (in GJ or MJ) for the building to the total interior gross floor area (in m2) of the building. The target value for a certain building is determined using a reference value and correcting it with the average climate correction ratio (CCR) for the location of the particular building. We have target values for various types of building usage. For a building with mixed usage, i.e. various types of building use in one particular building, each type of usage is taken into account with the percentage of the respective floor area for that particular usage, compared to the total floor area of the building. The CCR is calculated based on the climate correction with multi-year average Temperature Degree Days (TDD).
Climate correction with TDD
The energy use of a building, in particular for its heating, ventilation and air conditioning depends on the climatic conditions of the area in which the building is located. The energy efficiency target of buildings therefore takes into account the conditions of the climatic zone in which it is located.
In very cold areas and in hot and humid areas more energy is needed for heating or cooling and de-humidification of the outside air than in temperate climates. Also in areas with large differences between seasons, e.g. a cold winter and a hot and humid summer, more energy for heating, cooling and drying is needed than in zones with less difference between different seasons of the year.
What is the TDD Concept?
TDD concept quantifies temperature patterns for a specific local climate with respect to required indoor temperature conditions. It can be used to take into account different climatic conditions as well as for correcting weather variations in a particular year compared to multi-year (e.g. 5-year) average conditions.
TDD quantifies the daily measured differences between outside temperature and a reference temperature, accumulated for all days during a given period (e.g. a year). It is determined for heating (HDD) and for cooling (CDD).
At Novartis, Heating Degree Days (HDD) is defined as:
Sum of all ΔT (in ºC) for all days during a year with a daily average outside temperature θ below 18ºC (65ºF): ΔT = 18 – θ
Cooling Degree Days (CDD):
Sum of all ΔT (in ºC) for all days during a year with a daily average outside temperature θ above 18ºC (65ºF): ΔT = θ – 18
In order to cover not only heating and cooling, but also include de-humidification of outside air to specified indoor relative humidity conditions, we use CDD with a higher weight compared to HDD.
While the total energy need for heating and cooling normally is quantified as the sum of HDD+CDD, this approach intends including de-humidification by factoring in CDD with a weight of 2, i.e. HDD + 2 times CDD.
While this is a suitable approach for humid hot areas, it might over-account the drying needs for dry hot areas. However, it has the advantage of keeping the approach simple, and temperature data is much more available compared to humidity data.
The weight of x2 with which CDD is factored in has been determined by computer modeling energy needs for various HVAC requirements and for a range of climate conditions. The concept, the factor of 2 and the use of 18ºC as reference temperature was identified as a suitable compromise and is valid with an accuracy of 20 to 30%.
The climate correction applied for a specific location is therewith:
Total climate effect (TCEm): HDDm + 2 times CDDm and the
Climate correction ratio (CCR): TCEm (location) / TCEm (reference)
Note: The climate correction calculation is a largely simplified (potentially oversimplified) approach for various reasons. It is based on the assumption that the entire energy consumption is dependent on climatic conditions, which certainly is not true. Heating and cooling degree days are determined for nearby locations where data is available and not for the site itself. Local climate conditions may have a major influence.
How does Novartis determine the energy use performance of buildings?
The building energy use can be monitored with sub-metering of the respective electricity consumption in the building and primary energy (electricity or fuel) needed to generate heat/cold for the individual building. To determine a valid comparison to the target, the performance data can be corrected with the yearly weather correction ratio (WCR) for the location of the particular building, correcting changes caused by weather fluctuations. The WCR is calculated based on the weather correction with TDD.
Weather correction with TCE
The TDD concept can also be used for taking year by year changes of the local weather into account, by indexing actual energy use with a ratio of actual year TCE versus a multi-year (e.g. 5-year) average TCE. HDDa and CDDa values for actual year (with index “a” for actual) for a particular location are also available from the internet: http://www.degreedays.net/#
The weather correction ratio (WCR) is determined by: WCR = TCEa (actual year) / TCEm (multi-year average).
Note: This calculation is a largely simplified (potentially oversimplified) approach as it is based on the assumption that the entire energy consumption in the building is dependent on weather conditions, which certainly is not the case, as part of the energy consumption might be given from processes.
How does Novartis compare performance versus target?
The annual energy performance (energy consumption (in MJ) divided by the cross floor area (in m2), weather corrected (by dividing with WCR), is compared with the building’s energy efficiency target (climate adapted with CCR).
Target achievement is expressed as percentage of use compared to the target. For overachievement energy use is smaller than the target and the percentage is below 100%, for cases where the actual energy use is bigger than the target such percentage is bigger than 100%. The performance versus target percentage allows perusing improvements over time and serves as basis for benchmarking of buildings of different locations.
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