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Ventilation Systems

Chapter 11

Ventilation concepts

Natural ventilation – not assisted by a fan

Open windows and doors, considered sustainable

Mechanical ventilation – bring in air from outdoors; uses a fan to assist the process

Ventilation = supplying air without noticeable odors or pollutants to a space. Not just movement of air:

Air speed

Humidity

Odors

Pollutants

Indoor Air Quality (IAQ)

Indoor air quality – includes air movement (speed), humidity, pollutants and odors

Indoor relative humidity is 20%-60%

Environmental tobacco smoke (ETS)

Off-gassing – all synthetic materials emit chemical fumes, called volatile organic compounds (VOCs)

Humidity below 20% causes rapid evaporation, makes occupants feel cooler (rapid evaporation), become thirsty / dehydrated, body’s water is trying to achieve equilibrium with air in the room.

Above 60% feel sticky and uncomfortable, body’s reduced ability to evaporate perspiration.

Areas with a hot & dry climate can supply warmer air and still make occupants feel cooler, saves energy.

Primary ventilation system components

Fans – move air.

Ducts – what air travels in

Grilles & diffusers – covers at the end of ducts, disbursement

Filters – removes pollutants & odors

Humidifiers – increases moisture in air

Ventilation system (fans)

Fans – move air. Mechanical devices that push air through the system. Puts air in & takes air out. All fans require free movement of air. 2 types:

Supply fan-pushes air through duct system to space being ventilated

Exhaust fans-pulls air out of a space into the outdoors

Fan speed:

Slow air speed = air feels stagnant & stuffy, with high (RH) sticky feeling

Fast air speed = may feel too cool, blowing papers and other objects

Pressure:

Negative-air pulled in (back side of fan)

Positive –air pushed out

Ventilation system components (fans)

Pressure:

Negative-air pulled in (back side)

Positive –air pushed out (front side)

Ventilation system components

“DUCTWORK”

Ducts – channels, usually metal, through which air moves

May be round or rectangular

May also be referred to as a plenum

Supply and return ducts

Supply – supply air to the space

Return – removes and returns air to the heating/cooling coils, reconditioned and sent to the supply ducts

Ventilation system components

Dampers – metal slats, “mini-blind” like piece of equipment inside ducts, controls the air volume (amount)

Grilles

covers installed at the end of the duct (inside a room)

used on return ducts

Diffusers

used on supply ducts

uses louvers and directional slats to disperse air evenly; less breezy and quieter

Air filters

Mechanical filters

Only trap particles floating in the air

Paper media – disposable, usually 3 months

Metal or nylon washable and reusable

While these are initially more expensive than paper, they will save money over time.

Activated charcoal – adsorption; used in areas with a lot of smoke or odors.

Adsorption is a process where one substance sticks to another.

Not to be confused with absorption: one substance absorbs another like a sponge & water

Air filters

High Efficiency Particulate Arrestor(HEPA) filters – capture fine particulate matter as small as 0.3 µm.

Mechanical filters 20-30 µm, 1 inch = 25,400 µm.

Electronic filters – electrostatic charge causes pollutants to stick to metal plate.

One plate (+)charge, one (-) charge, particles receive positive charge, attracted to (-) charged plate

Ion-generating systems

A machine generates ions, which make dust and other pollutants stick to objects in the room or fall to the floor

Not recommended, due to potential problems for respiratory systems

Humidifiers

Used to add humidity to the air

Evaporative system – water trickles over a screen; air blows across the water, adding humidity

Atomizing system – a fine water mist is sprayed into the air

Caution: humidification systems need to be kept very clean, or you run the risk of mold, bacteria, or viral infection entering the airstream

Example: Legionella

Dehumidification: Chilled water or refrigerant cools air below dew point, condensation collects in the drain pain.

How much air (ventilation)?

Air supply is measured in terms of:

Volume -- cubic feet per minute (or cubic meters per minute)

Air changes per hour, usually determined by local codes

Number of times the rooms air volume is exchanged in a 1 hour period

Typically 5-20

Fresh air must be supplied to the building

Usually required to provide 10% - 30% fresh air (a.k.a., outside air or make-up air)

Design problem that results in air entrainment

Outside (fresh) air is brought into the building through a supply vent

Some of the used air must be exhausted out of the building, via an exhaust vent

Do not place the supply vent near the exhaust vent, or entrainment will occur

Exhaust air will get sucked back into the building, defeating the purpose of bringing in fresh air!

Getting the right amount of air to the space

Managing fan motor speed – use VVVF motor drive technology

Variable air volume systems – useful in providing the right amount of air to different rooms served by the same air handler

Good for offices, meeting rooms, public spaces

Not used for hotel guestroom systems

System balancing

Testing and adjusting ventilation system and air supply settings, due to changes or calibration concerns (age).

VAV & VF componets

Hotel guestroom ventilation

Many hotel windows cannot be opened

Guestrooms are not served by a package unit

Fan-coil units

PTAC units

Larger buildings/properties have a dedicated ventilation (exhaust) system, air shaft alongside each stack of restrooms.

Guestroom bathroom exhaust fan function?

Removes excessive humidity

Removes odors

Draws fresh air into the room from hallway/corridor

Corridor/hallway is red

Fresh air is supplied into the corridor. The exhaust system in each guestroom’s bathroom pulls air out of the guestroom and pulls fresh air under the door from the hallway.

The windows in the guestrooms do not open, so we cannot get fresh air into the room through the window.

Shutting off/limiting outside air

WHY?

Saves money, in the short-term, how?

Why Not?

Not code compliant, minimum 10%

Air becomes smelly, stagnant

Customer complaints, dissatisfaction

Loose market share, not repeat customers

Bad PR

Kitchen ventilation

Ventilation system maintenance

Motors – require regular preventive maintenance

Prolongs useful life

Increases energy efficiency

Reduces breakdowns and downtime for rentable space

Reduces risk of fire

Duct cleaning – you may need to have this done occasionally, depending on your property’s local conditions and usage

Ventilation system maintenance (cont.)

Drain pans – when air is cooled, it may be dehumidified

Water vapor condenses on the outside of the evaporator or chilled water coils

The condensate drips down into a drain pan

Drain pans can get clogged and overflow, leading to:

Flooding and mold growth

Microbial growth in standing water can become airborne, leading to mold, bacterial, or viral infections

Air filters can become soaked

Legionnaires’ Disease

The cooling tower is prime breeding ground for b. Legionella, the bacterium responsible for Legionnaires’ Disease

If your fresh air intake vent is located near the cooling tower, you may bring in air that is infected with b. Legionella

Cooling tower sanitation is critically important!

Many components of the HVAC systems can support the growth of dangerous bacteria

Hospitality Air Quality

Becoming more of an concern

Increased smoking ban on business (revenue)

One study air in typical hospitality venue was worse than the air a toll both collectors air

Standards for indoor air quality: ASHRAE standard 62

Ozonators

Generates ozone gases

cleans non-smoking rooms after someone has smoked

Not recommended by the EPA for treating air

Used to treat hot tubs, water features, kills bacteria

Myth 1

You can crawl through ductwork (probably not true)

Myth 2

Casinos pump oxygen into the air to wake up gamblers (it had better not be true)

Myth 3

You will suffocate if you get stuck in an elevator (definitely not true)