How to convert an existing building to a Nearly Netzero building

As per International Energy Agency 2017’s report, buildings sector uses one half of the electricity that is consumed globally (21 000 TWh) and accounts for nearly 8.67 GtCo2 emissions ie, one fourth share of total worldwide emissions. This undoubtedly stresses for need of some impactful activities to take up. At this juncture NZEB (Net zero Energy Buildings) / nZEB (nearly Zero Energy Buildings) concept has been found as an attractive option.

A Net Zero Energy Building (NZEB) is one which produces as much energy as it uses over the course of a year thereby reducing dependence on fossil fuel derived by increasing use of on-site and off-s energy sources. This concept focus on optimum utilization of building space for maximum renewable energy generation and overall reduction in energy usage through implementation of energy efficient systems.

Under energy efficient systems there were many opportunities in wide variety of areas like HVAC, lighting, overall power quality maintenance etc. Some ideas related to improvement in building energy efficiency quotient were as below:

Replacement of belt driven AHU fans with direct driven EC Fans

This technology is called electronically commutated brushless direct driven fans where in the losses at every stage from wire to air has been reduced considerably making the unit 15 - 20% more efficient than the belt drives. These fans will are having inbuilt speed control mechanism which further eliminates the need of VFD too.

Going for high COP chiller systems

Recent days with advancement in chiller technologies there arrived water cooled chillers which are having high COP’s in the range of 5.5 to 5.8. These chillers are having unique features like intelligent controls, magnetic levitation bearings, speed controlled compressors etc. 

Opting for Indirect evaporative cooling in place of vapour compression systems

Vapour compression is the refrigeration technique where in the dry bulb temperature gets reduced along with regulated humidity. Since it involves compression technique typical EER value will be around 2.5 - 3 w/w. In case of evaporative cooling the power consumption for delivering similar cooling capacity is 70-80% lesser as the energy consuming equipment are limited to blower and a water circulation pump.

Installation of Hybrid lighting systems

During day time, inbuilt double glazed Light collector receives sunlight over a large surface area and distributes light into the optical reflective system placed below it. This is built from highly reflective surfaces assembled in an Aluminium fixing system which guides the intercepted light to diffuser further below.

The high performance diffuser then spreads the daylight evenly without any glare or heat into the work space. The system’s daylight sensor continuously monitors the ambient sunlight. The electric lamps are divided into three groups each representing a step for switching on/off. If the daylight on task level is less than desired light intensity, called the set point, the controller switches on the required number of steps in electric lighting to achieve the set point, compensating the reduction of daylight.

Active Refrigerant Agents for chillers

Active refrigerant agent is an intermetallic compound technology which, when introduced into the refrigerant oil of a refrigeration system, forms a permanent bond to metal surfaces. This action removes oil fouling, changes the thermal nature of the metal and lowers the boiling point of the refrigerant gas, resulting in a more efficient operating system with substantial energy cost savings.

Waste Heat Recovery from Chiller & Utilize in Hot Water Applications

Facilities like hospitals, hotels etc., spends considerable amount of energy is hot water generation through different conventional energy sources. These facilities also uses major portion of electrical energy for catering its entire cooling load. Maximum cases this cooling load is delivered by chillers through vapor compression technology. Around 30-40% of total energy involved in the vapor compression system is waste heat. Low grade waste heat recovery systems are available in the market which can recover heat from the refrigeration cycle and can produce hot water at almost zero conventional energy input.

These low grade waste heat recovery systems extract heat energy from the high pressure vapor line going in to condenser through a simple modular heat exchanger. Amount of energy recovery depends on the refrigerant type and its temperature.A good amount of waste heat can be recovered when the discharge temperature of the refrigerant is more than 550C.Typical heat recovery will be around 15% of condenser load for ammonia based refrigeration system,10% for R22 based and 6 % for R134a based.    

And many other improvements like power factor improvement, unbalance voltage optimization, automation controls, water less cooling towers, speed control mechanism implementation for all major drives etc can be employed to help in satisfying the energy efficiency  quotient required to convert existing building to net zero energy buildings.

If required complete building can be powered up with the help of renewable power like roof top solar without working anything on energy efficiency, but this will be considered as uneconomical because without energy efficiency installation capacity of renewable systems goes up and demands for more space, more capital cost and  more maintenance. For example a building having an existing demand of say 100 kW can reduce its solar capacity from 100kW to say  70  80 kW if they convert existing systems to energy efficient systems since it’s not all about replacing energy sources but in turn reducing the usage of energy sources unnecessarily.

So in the process of converting an existing building to a net zero energy building the methodology to be followed is like first load analysis, energy efficient systems implementation, then load projections and finally installation of renewable energy sources.       

Technologies in RE:

Installation of Double sided solar PV systems

The standard solar panels have their rear surface made of plastic which caused the sunlight incident on the back side to go waste. The bifacial solar panels, on the other hand, have glass coating on both the front as well as rear surfaces. The design of these bifacial solar panels involves a glass-to-glass structure which makes it possible to capture the incidental reflective sunlight from the rear end along with the direct sunlight from the front surface. This allows them to produce more energy than regular modules. It’s been observed that these solar panels produce up to 20% more energy than the conventional mono facial solar cells of the same area.

The composite glass encapsulation of bifacial solar panels ensures higher durability, minimal degradation, and maximum service life. The structure is designed to protect the panel from environmental and mechanical damages. Thus, these panels often come with an extended warranty of 30 years, with their annual degradation rate being just 0.5%.

Going with Building integrated solar photo voltaics

Building integrated photovoltaics is the latest transparent glass used as a building material & as an energy-generating device, capturing the sunlight and transforming it into electricity. It is made up of 2 or more panes of heat treated, safety glass, which provides the same thermal and sound insulation, and natural light as a conventional architectural glass. Thus, this can be  installed in place of conventional glass on building facades, curtain walls, atriums, canopies and terrace floor, among others.

By providing similar thermal performance as that of a conventional glass, along with emission and cost free electricity from the sun, buildings can drastically improve their energy efficiency, decrease operational costs, and reduce their carbon footprint.

Hybrid solar mills

These are the systems which can harvest power both from solar and wind energy from its single system. These systems can generate certain amount of power even in the absence of sun lighting. Per Kw generation energy for these kind of systems is little high compared to conventional systems.

Duplex solar systems

These solar panels are having two compartments where in one generates electric power as usual and the second one beneath it will generate hot water simultaneously.

Generally solar PV modules will have an efficiency in range of 18 to 20 % which shows a loss of nearly 80%. This loss will be majorly dissipated in form of heat which is untapped. There are certain applications like hotels, hospitals and IT buildings with inbuilt canteen etc., where there will be requirement of both electric power and heat energy. In such applications these duplex panels supply both power and hot water by utilizing almost same space.

Above mentioned are some of the ideas to improve energy and RE quotient of existing buildings and converting them in to net zero energy buildings. As a first step first buildings can achieve nearly net zero energy where in the annual energy consumption will be less than 15 kWh/ sq mtr. Central government agencies like Bureau of Energy Efficiency (BEE) is also offering services like feasibility studies to convert existing buildings to net zero energy buildings. In near future even many incentives may also come up for this concept to boost up the implementation.