Q) Providing individual control for airflow & lights will help in

Accommodate individual preference in indoor comfort Better temperature control Monitor performance of building system Enhance indoor air quality

Q) Design Naturally Ventilated building such that adequate window opening are provided

Enhances thermal comfort Reduces energy consumptions Increases productivity Ensure minimum air ventilation

Q) Specify only eco-friendly refrigerant in the building air conditioning system

Better indoor air quality Energy efficiency Aid measurement & verification Reduce CFC release to atmosphere

Q) Insist on selecting air-conditioning chillers with COP that exceed requirement of energy conservation building code (ECBC)

Commissioning Higher Energy efficiency Maximum IAQ Performance Better Monitoring & Verification

Q) The energy conservation building code allows base building to assume air cooled chillers as the base-case for determining energy saving, as long as

Base load is met through water base chiller Chiller size is less than 5o tr Proposed building has installed air cooled chiller Proposed building has installed water cooled chiller

Natural Ventilation

Natural ventilation, also called passive ventilation, uses natural outside air movement and pressure differences to

both passively cool and ventilate a building.

Natural ventilation is important because it can provide and move fresh air without fans. For warm and hot

climates, it can help meet a building's cooling loads without using mechanical air conditioning systems. This can be

a large fraction of a building's total energy use.

Successful natural ventilation is determined by having high thermal comfort and adequate fresh air for the

ventilated spaces, while having little or no energy use for active HVAC cooling and ventilation.

You can choose the right strategy based on the temperature and humidity of your site. The following chart shows

how much these different strategies can extend the comfortable climate range for people.

Different passive cooling strategies can keep people comfortable at different ranges of outside temperature and

humidity.

This page includes

When not to use natural ventilation

Quantifying ventilation effectiveness

Air speed and temperature in buildings

Opening design

Thermal mass

When not to use natural ventilation

Sites with high levels of acoustic noise, such as near heavy traffic zones, may be less suitable for natural ventilation

because large openings in the building envelope can make it difficult to block outside noise. This can sometimes be

solved by using acoustical ventilation louvers.

Also, sites with poor air quality, such as adjacent to busy freeways, may also be less desirable for natural

ventilation. Such sites may overcome poor outdoor air quality with filters and ducting, though this usually requires

some mechanical fan systems.

Quantifying Ventilation Effectiveness

To measure the effectiveness of your ventilation strategies, you can measure both the volume and speed of the

airflow..

The volume of the airflow is important because it dictates the rate at which stale air can be replaced by fresh air,

and determines how much heat the space gains or losses as a result. The volume of airflow due to wind is:

Q_wind = K • A • V

Q_wind = airflow volumetric rate (m³/h)

K = coefficient of effectiveness (unitless, see below)

A = opening area, of smaller opening (m²)

V = outdoor uninterrupted wind speed (m/h)

The coefficient of effectiveness is a number from 0 to 1, adjusting for the angle of the wind and other fluid

dynamics factors, such as the relative size of inlet and outlet openings. Wind hitting an open window at a 45° angle

of incidence would have a coefficient of effectiveness of roughly 0.4, while wind hitting an open window directly at

a 90° angle would have a coefficient of roughly 0.8.

When placing ventilation openings, you need to place both air inlets and air outlets; often they do not have the

same area. The opening area used in this equation is the smaller of the two.

Air Speed and Temperature in Buildings

In addition to volume, you should design for the wind speed inside your building. Wind speed is a component

of human comfort, and the speed you want depends on the climate.

Higher velocity air causes more effective cooling, because it pulls heated air away faster, and because it helps

sweating be more effective by evaporating it faster. Even a moderate wind speed can cool perceived temperatures

5C (9F) compared to still air. This is how fans make people feel cooler even though they do not change the

temperature of the air.

However, the ability of air movement to cool people depends on whether it is the air itself that is hot, or if

the radiant temperatures of the room’s surfaces are hot. The hotter the air itself is, the less it helps to move it. If

people are primarily hot from surrounding radiant temperatures, however, moving air helps more. The ASHRAE 55

standard provides guidelines for how much cooling is possible with air movement at different speeds, for different

mean radiant temperatures. A 3°C temperature rise can be nullified by a 0.8 m/s increase in air speed when air

temperatures are 5°C below radiant temperatures, but if air temperatures are 5° warmer than radiant

temperature, it would require a 1.6 m/s increase in air speed. This is far above what is acceptable wind conditions

for light office work.

Comfortable air temperature vs. wind speed depends on mean radiant temperature

You’ll need to make sure that wind speeds inside the building aren’t so high that they disturb the occupants. Fast

winds can blow papers around on desks, blow people's hair around, etc (refer back to the Beaufort Wind Scale).

Referring to ASHRAE 55 for thermal comfort guidelines regarding air speeds for interior spaces, the standard

suggests that air speeds appropriate for indoor environments do not exceed 0.2 m/s or 0.447 mph. ASHRAE also

accounts for elevated air speeds that will increase the acceptable temperature. The maximum allowable elevated

airspeed is 1.5 m/s or 3.579 mph.

It is also important to consider how often the air in a room is replaced, as an important feature of natural

ventilation is that it supplies occupants with fresh air. The number of times the air in a room is replaced is known

as air changes per hour, ACH, or the air change rate. It is determined by both the size of the room and the

volumetric flowrate of air (Q). Q_wind, referenced above, is a component of this overall flow rate.

There are standards and recommendations for how much fresh outside air should be delivered to different

building spaces, and to people within the building. For example, ASHRAE 62.2001 specifies 0.35 air changes per

hour for residential living areas, but also specifies a minimum volumetric flowrate of 15 ft3/min (CFM) per person.

The equation is:

ACH = (Q / V) * (conversion factor)

Q = volumetric flow rate of fresh air

V = Volume of room or space

Conversion Factor = If the volumetric flow rate, time scales, and volumes are incongruous units. For example, if Q is

in cubic feet per minute (CFM) and volume is in ft2, you’d need to multiply by 60 to get it in terms of hours. If Q is in

cubic meters per second, or Liters per second, the conversion factor would be different.

Opening Design

Window design and ventilation louver design greatly affects the airflow. Windows that only open halfway, such as

double-hung and sliding windows, are only half as effective for ventilation as they are for daylight. Some casement

windows and Jalousie windows, however, can open so wide that effectively their entire area is useful for

ventilation.

Casement windows can deflect breezes, or can act as a scoop to bring them in, depending on wind direction.

Jalousie windows (horizontal louvered glazing) can catch breezes while keeping out rain.

Some window types: double-hung, jalousie, and casement

You can also use ventilation louvers instead of windows for your openings. Their coefficients of effectiveness will

be the same as windows of the same geometry, such as Jalousie windows. Ventilation louvers often open so wide

that nearly all their area is useful for ventilation. They are typically oriented horizontally to prevent rain from

entering; this is an advantage over most windows. Ventilation louvers also provide visual privacy, and can even

provide acoustic damping.

Mechanized and acoustically-damping ventilation louvers

Opening Shape

Opening shape matters as well. Long horizontal strip windows can ventilate a space more evenly. Tall windows

with openings at top and bottom can use convection as well as outside breezes to pull hot air out the top of the

room while supplying cool air at the bottom.

Opening Size

Window or louver size can affect both the amount of air and its speed. For an adequate amount of air, one rule of

thumb states that the area of operable windows or louvers should be 20% or more of the floor area, with the area

of inlet openings roughly matching the area of outlets.

However, to increase cooling effectiveness, a smaller inlet can be paired with a larger outlet opening. With this

configuration, inlet air can have a higher velocity. Because the same amount of air must pass through both the

bigger and smaller openings in the same period of time, it must pass through the smaller opening more quickly.

(See the physics of the Venturi effect.)

Pairing a large outlet with a small inlet increases incoming wind speed.

Note that a small air inlet and large outlet does not increase the amount of fresh air per minute any more than

large openings on both sides would; it only increases the incoming air velocity. Basic physics says that air cannot

be created or destroyed as it moves through the building, so in order for the same amount of air to pass through a

smaller opening, it must be moving faster.

Air flows from areas of high pressure to low pressure. Air can be steered by producing localized areas of high or

low pressure. Anything that changes the air's path will impede its flow, causing slightly higher air pressure on the

windward side of the building and a negative pressure on the leeward side. To equalize this pressure, outside air

will enter any windward openings and be drawn out of leeward openings.

Because of pressure differences at different altitudes, this impedance to airflow is significantly higher if the air is

forced to move upward or downward to navigate a barrier without any corresponding increase or decrease in

temperature.

Thermal Mass

Thermal mass can also have an impact on natural ventilation. Sometimes a space can get too hot for natural

ventilation to have an impact on thermal comfort. However, you can use thermal mass to help maintain a

consistent temperature and avoid big jumps. By stabilizing the temperature swings, you have a better chance of

using natural ventilation effectively. Best practice design strategies for enhancing natural ventilation with thermal

mass is explained further through night flushing.

Dive Deeper

Wind VentilationWind ventilation is a kind of passive ventilation, using the force of the wind (or local air pressure differences) to pull air through the building. Wind ventilation is the easiest, most common,and often least expensive form of passive cooling and ventilation.

Stack Ventilation and Bernoulli's PrincipleStack ventilation and Bernoulli's principle are two kinds of passive ventilation that use air pressure differences due to height to pull air through the building.Lower pressures higher in the building help pull air upward.

Night-Purge VentilationNight-Purge Ventilation (or "night flushing") keeps windows closed during the day, but open at night to flush warm air out of the building and cool thermal mass for the next day.Night flushing is only suitable for climates with a relatively high temperature range from day to night,like the desert.