Buildings that are intended to provide indoor air quality that is acceptable to human occupants and minimises adverse health effects. Various fans and air circulating devices are used to achieve this objective. Obviously, it consumes very high amount of electrical energy. Whereas changes to the 2013 ANSI/ASHRAE edition of the standard primarily focused on usability and clarity, the 2016 edition includes a major change to the scope of the standard by which residential occupancies are moved from Standard 62.1 to Standard 62.2.
The Importance of Indoor Air Quality
On average, people spend 90 per cent of their time indoors, so clean indoor air is essential for optimum health. Sadly, many homes and businesses have contaminated air.
Volatile Organic Compounds (VoCs), pollen, radon gas, smog, mold (Mold is a key factor in breaking down organic matter such as fallen leaves and dead trees. That is good for outdoors, but not for indoor), fumes, and odours all degrade home air health. Indoor air pollution can be especially a matter of concern for people who have chronic diseases, compromised immune systems, or mold or chemical sensitivity.
Energy Efficiency & Comfort Conditioning
Most ventilation systems drive up heating and cooling costs while decreasing indoor comfort. Much like venting a room by opening a window, ventilation systems can degrade energy performance because they exhaust air without capturing the heat. Because exhaust fans need makeup air to operate properly, they pull in unconditioned air through gaps and cracks in the building exterior, creating drafts. This has a huge impact on both comfort and energy costs.
Heat Recovery Ventilation (HRV) and Energy Recovery Ventilator (ERV) systems conserve energy, lowering utility bills. The heat from the exhaust air is transferred to the incoming air via a heat exchanger. Zehnder heat recovery ventilators are up to 95 per cent efficient, saving energy. This also helps to reduce the size of the HVAC equipment needed because it doesn’t have to work as hard to heat and cool when the intake air is conditioned by the HRV unit.
An HRV provides a constant supply of fresh filtered air for the building’s occupants. The higher the heat recovery percentage, the greater the comfort. For example, if the indoor room temperature is 70 degrees Fahrenheit and the outside temperature is 30 degrees, the heat recovery rate could mean the difference between having air in the low 60s coming into the house versus air that is over 65 degrees. Less efficient HRV systems can supply fresh air to living spaces at uncomfortable temperatures. As a result, occupants turn off the unit or use it intermittently. This is a concern because, without the constant ventilation, indoor air quality will suffer.
Ventilation Strategies for Passive House Certification
A Passive House is a building in which thermal comfort can be provided solely by post-heating or post-cooling of the fresh air flow which is required for good indoor air quality.
The Passive House Standard, a voluntary standard for ultraenergy-efficient homes and buildings is at the forefront of energy conservation. In fact, projects built to this standard are 80 per cent more efficient to heat and cool than a typical new building built to the minimum building code requirements. Most Passive House projects feature an ultra-energy-efficient envelope with continuous insulation and meticulous air sealing. Passive House construction in colder climates typically requires triple-pane windows, generous amounts of insulation, and heat recovery ventilation. Because little air is allowed to leak in or out of the building, a mechanical ventilation system is essential to protect indoor air quality.
In addition, ECBC or GRIHA or LEED for Homes awards two points to projects that go beyond basic ventilation measures and installs a system that provides heat transfer between the incoming outdoor air stream and the exhaust air stream. An additional point can be earned by projects that undertake commissioning to verify that ASHRAE 62.2 ventilation requirements are being met by the ventilation system.
Using HVI Ventilation Standards
The Home Ventilation Institute or HVI, recommends that an HRV or ERV (Heat & Energy Recovery Ventilation Units) provide at least 0.35 air changes per hour throughout an entire home. This translates to about five cubic feet per minute (CFM) per 100 feet of floor space. For a 1,000 Cufoot home, this standard requires a continuous ventilation rate of 50 CFM-although this may vary depending on the number of occupants in the home.
For best results, the ventilation system that is chosen should be capable of slightly higher rates of circulation than this minimum. Large gatherings and activities that produce airborne VOCs may create a need for higher air exchange rates to maintain air quality. Bathrooms and kitchens may require higher ventilation rates and may benefit from having returns or fans placed strategically to remove warm, moist air.
Using ASHRAE 62.2 Standards
ASHRAE stands for American Society of Heating, Refrigeration, and Air Conditioning Engineers. The organisation creates detailed ventilation standards that dictate what proper air exchange should be in a variety of different settings. These standards are very useful for businesses, as areas like game arcades, lobbies, warehouses, commercial kitchens, and hospital waiting rooms may all benefit from having different levels of air circulation.
ASHRAE standards are also useful for private residences and apartments and can be used by construction companies to ensure a new or renovated building is up to par. ASHRAE standards are highly complex and take occupancy rates and other factors into consideration to determine optimal ventilation. Updated standards are also being released for 2016. In order to use ASHRAE standards to determine your home ventilation needs, it is best to consult a ventilation expert.
Solar Passive Ventilation for comfortable indoor quality
Using Passive House Standards
Passive House standards dictate the airtightness level of a home using an onsite pressure test to gauge the air seal. The home must not exceed 0.6 air changes per hour before ventilation has been installed in order to ensure that air quality is strictly controlled. Passive house standards dictate energy usage so heat and energy recovery ventilation is the key to meeting all standards. ERVs and HRVs installed in passive homes help to make sure that at least 75 per cent of the energy is transferred from outgoing air to incoming air. Ventilation is carefully controlled to reach a rate of about 0.4 air changes per hour.
Diagram A: Solar Passive Ventilation for comfortable indoor air quality
We must be aware of local regulations and codes.
Fresh air supply – make up air – to a room based on the table above can be calculated as
q = n V (1)
q = fresh air supply (ft3/h, m3/h)
n = air change rate (h-1)
V = volume of room (ft3, m3)
Example – Fresh Air Supply to a Public Library
The fresh air supply to a public library with volume 1000 m3 can be calculated as
Q = (4 h-1) (1000 m3)
= 4000 m3/h
Practical Installing Cases
The attached drawing ‘A’ shows the principle of the Solar Passive Ventilation for hot regions typically for a residential house.
The ducts made up of 18 swg GI sheet of size 300×300 mm c/s these ducts are fitted with louvers, the opening or closing of which can be adjusted by pulling the hanging strings. These ducts are painted as per the aesthetic need of the room. The ducts emerging from various rooms are brought at on place near the convenient centre of the building. A puncture is made to the RCC slab. A chimney of size 600×600 c/s and height of 3000 mm made up of 16 swg GI sheet is erected on the roof which is painted with mat black heat absorbing paint. On top of the chimney, a turbo ventilator is fitted for efficient flow of hot air and avoid in grace of rain water or any other insects. The windows can either be kept closed or can be provided with inlet having wood wool with slow water drip humidification (WWH) (similar to desert cooler), this would further lead to better cooling effect.
Principle of Operation
The chimney on the rooftop gets substantially heated up and inside air moves due to thermo syphon effect. The turbo ventilator accelerates this air circulation rate. Now, obviously the space inside chimney pull the air from the ducts i.e. from the various rooms. Thus, the air from rooms is sucked and thrown outside due to simple thermo-syphon effect. The outside air is sucked in through the gaps of windows and doors. In addition to intake of fresh air this develops a slight negative pressure in the room and the temperature drops down offering cooling effect. If the WWH system as explained above is provided then it would lead to further higher cooling effect.
Live Case Study
• Punjab Energy Development Agency (PEDA) building at Chandigarh in India is a remarkable example of this in business or commercial building (Photographs are attached). Ministry of New and Renewable Energy Sources (MNES-GoI) is encouraging such type of Solar Passive Ventilation through their all State Nodal Agencies viz. PEDA, MEDA, CREDA, GEDA, NEDCAP etc. it is also encouraged by Bureau of Energy Efficiency (BEE), LEED, ECBC and GRIHA Rating.
• At Masdar university in UAE, they have erected a tower in an open space surrounded by academic buildings. The ventilation in an open area is worth experiencing and studying.
• There are some residential houses also having adopted this concept located in Aurangabad, Dhulia of Maharashtra and Rewa of Madhya Pradesh.
Future Scope for R&D
The above explained concept has been successfully proven for cooling application.
It is necessary to try and evaluate the performance for heating application in cold zone or during winter for room heating application. If the top ventilator is supplemented with a solar powered fan to push the air downwards and the tower wall is provided with heat exchanger fins from inside then the air will get heated due to heat of the tower and it will get spread into the rooms. This would substantially reduce the use of room heating load using electricity. The room heated throughout the day time would retain the heat after sunset and only during early morning hours artificial heating source may be required.
If the walls of the tower are provided with heat retaining material, the cooling and heating function can be extended for full night also.