Occupant perspectives: NZEB at CEPT University – CARBSE

An operational net-zero building in a hot-dry climate

The Centre for Advanced Research in Building Science and Energy (CARBSE) in CEPT University, Ahmedabad houses some of the world’s most cutting-edge research in energy-efficient building design. At the same time, it’s a living laboratory in itself, operating as a net-zero energy building. As a result, the building provides invaluable lessons in designing, constructing and operating a net-zero energy facility.

This webinar brings on board two experts from CARBSE, Prof. Rajan Rawal – Executive Director and Dr. Yash Shukla – Technical Head. They bring their expert insights and rich experience of designing, occupying and managing an exemplary Net Zero Energy Building in India.

CARBSE at CEPT University, Ahmedabad

CARBSE was conceived as an exemplar of net-zero energy design strategies and technologies specific to the Indian climate. The model NZEB would thus be the perfect setting to conduct research on high-performance building design, tech and policy.

The team was committed to an integrated design approach to maximize synergies across disciplines and expertise. Through an iterative process, the team arrived at an Energy Performance Index (EPI) target at 58 kWh/sqm/yr for CARBSE. Various passive and active measures were integrated into the building design to achieve the ambitious EPI target. Let us take a closer look at these measures.

Firstly, the building was oriented towards the South with a sloping roof to accommondate the solar PV. Next, the team analyzed several massing options for the arrive at the design with the least heat loads and corresponding energy consumption.Building envelope optimization ensured further reduce heat ingress. The façade with thermal mass and insulation offer high thermal resistance and lag during hotter months. The low-e double glazing unit with a Visual Light Transmittance (VLT) of 39% ensures optimum daylighting without heat gain. Clearstory windows with a VLT of 33% provide glare-free north lighting. Light shelves reflect daylight deeper inside the workspace. Occupancy controls and daylight sensors enable a Lighting Power Density (LPD) at 4.7 W/sqm.

Passive design strategies in CARBSE

A mixed mode space conditioning system has been designed for CARBSE. For example, the basement uses a VRF system while the ground floor is naturally ventilated. The first floor and mezzanine can switch between mechanical and natural modes. Space cooling is also provided by a radiant system. Ventilation requirements are met through natural ventilation as well as a dedicated outdoor air system (DOAS).

Dr. Yash shares several practical insights into ensuring CARBSE’s NZE status through the years. We learn that CARBSE is intensively monitored all year, equiped with 1000 control points to monitor indoor environment, envelope, energy consumption, occupant comfort, equipment end-use, etc hrough a state-of-the art Building Management System (BMS) system. The data is displayed on an LCD screen in real-time. Components like energy meters, photovoltaics and chillers can be easily integrated with the BMS as they come pre-fitted with sensors and controls, and only need a communication gateway. However, for components like lighting, DOAS and fans, the team had to install sensors and controls before integrating it with the BMS system.

The experts shared monitored data of 2016-17 where HVAC energy use was 24.1 kWh/sq.m/yr followed by research equipments consuming around 15.5 kWh/sq.m/yr. Plug loads were very low at 2.7 kWh/sqm/yr while the daylighting strategies were succesful in reducing the lighting energy merely 0.1 kWh/sq.m/yr. In that year, CARBSE was energy positive with consumption is at 42.5 kWh/sq.m and generation at 51.2 kWh/sq.m

Monitored data shows that the indoor temperatures are within the 80% and 90% acceptibility limit as per the Indian Model of Adaptive Comfort (IMAC) model indicating that it is possibe to acheive thermal comfort standards while reducing the energy use. Further, thermal comfort is also assessed through weekly surveys for qualitative feedback from occupants.

To summarize, CARBSE shows that climate responsive design strategies can help achieve comfort with less energy use. The data clearly demonstrates that occupants feel comfortable in the temperature range as per the IMAC criteria. This approach alongwith passive strategies and efficient mechanical systems has sharply reduced the energy demand which is met with rooftop solar PV systems making this a ‘high-performance NZEB’. It underscores the need for continuous monitoring and measurement to maintain the net-zero energy goal.

This webinar was conducted on 23 July 2019.

Rajan Rawal | Executive Director, CARBSE

Prof. Rawal is the Executive Director of Centre for Advanced Research in Building Science and Energy (CARBSE). He is an architect and his work emphasizes on ‘energy performance of buildings and cities’ and ‘architectural science education’. He is involved in research and development activities at CEPT University and coordinates the activities of CARBSE. He is founder member secretary of India Chapter of International Building Performance Simulation Association (IBPSA) and also serves at IBPSA world committee. He has number of research papers, technical reports and three books to his credits. Prof. Rawal is a well known authority in the area of building energy efficiency and performance.

Dr. Yashkumar Shukla | Technical Director, CARBSE

Dr. Shukla is the Technical director at CARBSE and also an ECBC Master trainer. He is a mechanical engineer with more than fifteen years of international experience in building energy-efficiency research and serves as a lead on several energy-efficiency research projects at CARBSE. He has extensive experience in building management systems, building energy analysis, HVAC system operation, component characterization facilities, development of test chambers, building simulation modeling, and energy efficiency control algorithms. His prior work experience also includes providing technical support in designing and implementing commercial and residential energy-efficiency programs throughout the US.

Q1. Can buildings of different scales and application target Net Zero?
Provided that the building has enough capability to generate energy from RE sources, it is possible to target Net Zero for different scales but application wise it is not as straight forward. Applications with a high demand load can make targeting net zero very challenging. Reducing demand is the key factor that needs to be looked at.

Q2. What was the criterion to keep the CO2 level trigger point at 1000 PPM for outdoor air exchange when it’s recommended that indoor CO2 level should not exceed 700 PPM of CO2 for sustained periods?
As per the ASHRAE standards, the indoor CO2 level threshold for office buildings is 1200-1500 PPM depending on how stringent the designer wants to be. But we approached CEPT design aggressively in wanting to capping the indoor CO2 level at 1000 PPM.

Q3. When it is too hot outside, is the indoor air still exchange with the outdoors to maintain a favorable CO2 level?
Yes. Health is the priority and hence if the CO2 level reaches the threshold level, we exchange indoor and outdoor air. If the outdoor environment is harsh, the windows are shut and the air ventilation is done through inlet and exhaust fans.

Q4. As this is a mixed mode building, are the windows operated mechanically or manually?
The windows are operated manually.

Q5. Is the building used 7 days a week?
Typically it’s .5-6 days a week.

Q6. Any reason for not installing ceiling fans?
Radiant ceilings along with ceiling fans wasn’t considered as an ideal combination. Radiant ceilings provide a horizontal air movement versus the vertical air movement of ceiling fans.

Q7. Can space heating during winters also be achieved naturally without heating coils or heaters?
While the system is capable of providing heating, there has been no heating required during winters between 2014 and 2019. Because the building is an area where it doesn’t get too cold outside and the building envelope is with a high U-value, there has been no need for the heating system.

Q8. What was the chiller size for the radiant and VRF system. Was it difficult to find a chiller that would work at such low full-loads and then part loads as well?
Yes. It was a huge challenge to find inverter or variable capacitor chillers for the design size. Few European manufacturers were engaged, and they provided the low capacity chillers. Another criteria which played a big role was the compatibility of the chillers with the BMS.

Q9. How many occupants are there in the building?
On any given day, there are 30-40 occupants on the researchers’ floor. And occasionally (60-90 days in a year), there’ll be 60-100 occupants in the conference and seminar rooms for an hour or so.

Q10. Any strategies for accommodating an increase in occupants in the future?
No, there are no strategies.

Q11. What is the capacity of the PV system?
The rooftop PV system is 30 kWp.

View webinar presentation – Insights into CARBSE

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