CM 3201 Week 3

Heat Transfer/heat

(_________________) occurs at heat exchange section of the air hauling unit. Depending of the medium, ________ is transferred through one or a combination of components.

Various Systems for Zone Control: Constant (CV)

- Constant Temp, Variable Volume (on/off) - Single Zone CV - Single Zone Reheat CV - CV Terminal Reheat - CV Dual Duct and Multizone

Air Handling Unit Components

- Fan sections, for supply air and return air/relief air fans - Cooling section, for chilled-water or refrigerant cooling coils - Heating section, for hot-water or steam coils, a gas heat exchanger, or an electrical coil - Humidification section for extra humidity, if required - Filter sections, for prefiltering, filtering, and post-filtering - Air-mixing section, for outdoor air to mix with recirculated air - Discharge air plenum - Other components, for electrical power, controls, operating a motor, drainage, etc.

Ways to Save Energy

- Most basic way to do this is to shut down unnecessary equipment. - operating parameters of systems and equipment can be adjusted to same energy. - operating equipment at optimum conditions - Monitoring building electrical demand and shutting down equipment to prevent consumption from exceeding preset limit. - Record equipment trends

Variable Refrigerant flow (VRF)

- Similar to fan coils but use refrigerant coils. - Uses fan coils and does not need duct work

Fan Coils

- Small version of AHU - consists of a filter, a cooling and>or heating coil, a fan, and controls. - can be located above the ceiling, in wall cabinets, or in soffits. - Run off piping system - Used to provide multiple zones of contrast - two pipe of four pipe system

Fan Laws

- The system resistance increases with the square of the airflow rate. - For the same fan size and system, the airflow rate varies directly with the speed, the pressure varies as the square of the speed, and the horsepower varies as the cube of the speed. - For constant speed and varying fan size, the flow rate varies as the cube of the fan size, the pressure varies as the square of the fan size, and the horsepower varies as the fifth power of the fan size.

VAV Terminal (Boxes)

- contain dampers that vary the airflow to individual zones of control in response to their thermostats. - can serve large, complex buildings, offering the flexibility of being able to add or rearrange zones by adding or rearranging terminals on the main trunk ducts. - inexpensive and energy-efficient. - used extensively in commercial and institutional buildings. - Would need an additional system to include heating process.

Single Zone VAV

- energy-efficient alternative to constant-volume terminal-reheat and constant-volume dual-duct system - cooling: vary the quantity of air supplied to the space in response to the space thermostat. - AHU supplies chilled air. If the cooling load is high, the chilled airflow will be high. As the load diminishes, the airflow is reduced accordingly. No energy is wasted by reheating or mixing warm and chilled air. - use a cooling coil to produce chilled air at a constant temperature. - Airflow is increased or decreased in response to the space thermostat by adjusting dampers or the speed of the fan. - Such a unit may also be equipped with an additional coil for heating - Can serve only 1 zone - Small buildings or single zones within a large building.

Baseboard Convectors

- excellent at preventing downdrafts under windows. - used as a source of heat in conjunction with VAV terminals for cooling. - use electric resistance elements or hot-water piping equipped with fins to enhance heat transfer (Finned tube convectors)

Variable Flow Diffusers

- operate by opening or closing diffuser blades in response to remote thermostat or integral temperature controller. - Can be used in lieu of VAV terminal in spaces small enough that don't require use of VAV terminal - can be used as basis for entire building system depending on how you design the system. - switchover feature to. provide either cooling or heating

Variable Frequency Drives (VFDs)

- reduce electrical energy consumption by adjusting a motor's speed to match the required load. - control the equipment's output to match the operation's needs, saving energy when full output is not required. - eliminate the need for expensive and energy-wasting throttling mechanisms such as control valves and outlet dampers. - "soft-start" capability that gradually ramps up a motor's operating speed at startup and greatly reduces the stress on components. - can improve process efficiency and occupant comfort. For example, ________ allow greater control of machine tool drives and processes such as water distribution, aeration, and chemical feed

Constant Temp, Variable Volume (on/off)/ Forced Air

- typically seen for common residential forced air type of system - Activates when temperature rises above, or dips below a set activation point. - Supplies hot or cold air to space until the set temperature point is reached. - Volume of air supplied to a space depends on how long fan is activated. - Supply Temp Fairly Constant. Process: - Electronic or gas furnace that has fans that heat the air with the gas or the electric source and force it through the duct work to a conditioned space. A split A/C unit that includes a condenser outside the home and refrigerant lines to connect to furnace inside the home. The Furnace then forces the cool air through the ductwork to condition the space. At this point, when its using the furnace to move it through, all your using is the fans and the blowers within the furnace. You are not actually turning on the heating source. So its still just moving around the air, you're just not heating it up like you would in the winter.

Multiple Zone VAV

- use a VAV air-handling unit to supply chilled air into a main trunk duct feeding multiple VAV terminals that in turn serve individual zones of control. - Uses VAV terminals - Used extensively in commercial and institutional buildings

Package Terminal Air Conditioners (PTACs)

- window or through-wall units containing their own compressors and air-cooled condensers - can be installed with or without electric heat and may be designed as heat pumps for more economical operation. - limited to rooms with outside exposure or spaces with suitable adjacent places to reject heat from refrigeration. - tend to be noisy and require high maintenance as their compressors age.

Equal Friction Method

-Easiest Duct sizing method with quick results -Requires dampers to balance system -Used in small to medium type facilities

How Air Filters are classified

1. Filtration principle. Filtration by the medium or by electrostatic precipitation. 2. Impingement. Dry medium or viscous impingement. 3. Configuration. Flat or extended surface (pockets, V-shaped or radial pleats). 4. Service life. One-time disposable or renewable. 5. Performance. Low and medium efficiency,high-efficiency particulate air (HEPA), or ultrahigh efficiency (UEPA). 6. Special features. Odor absorption, disposal of radioactive material, etc.

Which duct would you choose after converting from round to rectangular, in order to reduce ceiling height? 20"x14"x10' or 15"x18"x10' ?

20"x14"x10'

Direct Expansion System

3 lines to look at: RS: Refrigerant suction lines RHG: Refrigerant hot gas line RL: refrigerant liquid line

Air Handling Unit (AHU)

A device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. -

Single Zone (CV)

Air is supplied to the space at a constant rate. The air-handling unit includes a cooling coil and/or a heating coil that varies the temperature of the air in response to a space thermostat. Heating and cooling may be on-off or proportional - Simplest of systems - 1 thermostat controls entire zone - Difference between this system and the forced air system is that the single zone uses water and coils to heat or cool air by passing air over to coils filled with cooled or heated water - great for small simple buildings such as offices or large open spaces such as warehouses. More for commercial use

Particle Size Efficiency Test

Atmospheric dust is fed into the air cleaner, and air samples taken upstream and downstream are counted to determine the efficiency of removal of each size of particle.

Dust spot efficiency test

Atmospheric dust is passed into the air cleaner, and the discoloration is observed.

Steam Coils

Coils who's tubes are designed for easy drainage of condensate. - Two types: - General Purpose (conventional type) - Steam Distributing

Coanda Effect

Cold air clings to the ceiling upon being discharged from the diffuser. Allows air stream to fall gradually and mix with the room air over a large area

Static Regain Method of Duct Sizing

Duct sizing method where: - Adjust duct size to obtain equal static pressure and correct air quantity at each outlet - Most accurate method to sizing a balanced duct system - Involves many calculations for each fitting and duct section -Used for large distribution systems

4 Tests for rating Air filter efficiency

Dust weight arrestance test Dust spot efficiency test Fractional Efficiency Test Particle Size Efficiency Test

3 major operating characteristics of air filters

Efficiency Resistance to air flow Dust Holding Capacity

Electrical Coils

Electrical coils may be designed as a part of the air-handling unit or may be installed on the ductwork exterior to AHU - heating elements are usually made of a nickel-chromium alloy.

Automatic Controls

Enable equipment system to operate more precisely and reliably for comfort. safety, and energy efficiency. They accomplish this by controlling one or more of the 6 properties of transporting medium (air/water) and related equipment.

Economizer Cycle

Feature that allows increased amounts of outside air for free cooling to avoid operating refrigeration equipment. - involves controlling the position of the outside and return air dampers so as to result in a mixed air temperature that will supply cooling for the building— generally, 55-60°F.

Automation

Function of having equipment react without. any intervention by an operator to satisfy preset conditions.

Direct Digital Control (CDC)

Instead of physically adjusting the controller, components to result in same reaction over and over again, it contains microprocessors, which are programmed to interpret the input signal, process the data in resident programs, and intellectually decide on appropriate response.

Series Loop System

Maintenance/repair requires shutdown. Temperature control at each unit is impossible Number of units served limited only heating or cooling

Small Air Handling Unit

May only consist of a supply air fan, coils, and an air filter.

Water coils

Most common component for transferring heat with circulating air. - normally constructed with copper tubes and aluminum fins. - Performance depends on the design of its tubes and fins, as well as the size of the coil, including the depth and face area.

Air mixing

Outside air required for a building is usually ducted to the inlet of an air-handling unit by mixing with the return air. The two airstreams must be balanced with dampers to introduce sufficient outside air for ventilation, but not so much as to require excessive conditioning during extremes of weather.

Dust weight arrestance test

Particles of synthetic dust of various sizes are fed into the air cleaner (filter), and the fraction by weight of the dust removed is determined.

Controls and Automation

Provide the intelligence of mechanical and electrical systems. Make the equipment operate under all anticipated conditions.

When converting from ____________ to ____________, find the smallest size to reduce ceiling height and material needed.

Round to Rectangular

VAV Multizone

Separate dampers are used for the warm and cold portions of the mixing section (see Fig. 3.23). The cold-air damper is almost closed before the warm-air damper is allowed to open. This prevents energy waste due to mixing.

Classifications for Ductwork

Seven classes based on SMACNA regulations - Based on pressure ---> Measured in inches of water column (w.c.) - 1 w.c.= 0.036 psi- Based on velocity flow of air-----> Measured in feet per min Table (6.3)

Rectangular Duct

Shape of duct where width of the ductwork is stated 1st. for example: 20" x 14'" = 20" wide, 14" height

Reverse Return System

System in which water flows through multiple units of HVAC equipment and is inherently balanced.

6 properties of transporting medium controlled by automatic controls:

Temperature Pressure Flow Rate Humidity Speed Time

Over pressurizing a Building

Tends to happen when large quantities of outside air for ventilation or free cooling are brought into a building via the economizer cycle.

DDC thermostats

Thermostats that can share info, decide to cool or heat on its own

Return Air fans

These fans may be part of the air- handling unit or may be installed separately in ductwork upstream of the unit. - Can be centrifugal or axial and do not need to be the same as supply fans

Fractional Efficiency Test

Uniform-sized particles are fed into the air cleaner, and the percentage removed by the cleaner is determined.

Hybrid VAV System

Usually contain Multiple Zone VAV systems in the center, or core, of the building, while convectors, such as baseboard convectors, at the exterior areas. (Assignment question)

Constant Volume of Air (CV)

Varies Temperature while keeping air flow constant. Typically uses variable conditioned air temperature (monitored at the thermostat) to maintain room conditions. Air volume typically remains at a constant rate. - when fans run continuously to provide ventilation while the building is occupied

Variable Air Volume (VAV)

Varies the volume of warm or cold air supplied while keeping the temperature constant. Air volume varies (monitored at the thermostat) to maintain room conditions. Conditioned air temperatures are constant.

Direct Expansion Coils (DX)

When the cooling medium is a refrigerant (e.g., Freon), the cooling coil is designed to allow the refrigerant to vaporize in the coil, thus absorbing heat from the air. - consists of a refrigerant header and many distribution tubes. The tubes may be single circuited for small coils or horizontally and vertically split for even distribution of the refrigerant to the coil depending on the performance required.

When Energy Savings are highest for VFDs

When used with variable-torque loads, such as fans and pumps for HVAC purposes. The best applications are large motors that can operate for many hours at reduced speeds, such as fans for cooling towers, where loads vary from season to season and from day to night.

Air movement created by fan

Without this, cool air tends to be stagnant and cause condensation of moisture on room surfaces.

Chilled Beams

a flush, or surface mounted ceiling device containing chilled water coil. - operate without fans, relying on convection and induction of room airflow by flow of the ventilation air.

Fans

a mechanical device that moves air used in HVAC systems to ventilate or transport heat or cooling. - have a rotating impeller with blades; this in- creases the kinetic energy of air by changing its velocity. The increased velocity is then converted to pressure.

One Pipe System

allows for each Unit to be controlled. However, you can't divide up the cost of utilities. Based on one central unit for entire building. Limited number of units can be served. Needs Special fittings. Only Heating or cooling.

Zone

an area for which temperature is controlled by a single thermostat. Can also apply to areas of humidity control. These are NOT rooms.

Drain Valves

are installed at equipment and at the low points of piping systems. Hose end fittings are normally used, and fluid is conducted to the nearest floor drain. Floor drains are required in mechanical rooms and should be placed close to condensate discharge from cooling coils to avoid piping over the floor. This is generally a convenient location for draining hot- and chilled-water coils.

VAV Dual Duct Terminals

arranged for operation at a variable rather than a constant air volume in order to conserve energy.

Dampers for air mixing

arranged to force the two airflows to collide, with turbulence for good mixing.

Air filter resistance

can be reduced when the design airflow rate is lowered. In general, the filter man- ufacturer provides a range of face velocities and initial and final resistances for each type of filter.

Mixing Box portion of AHU

carefully designed to prevent stratification of cold outside air in winter, which could freeze the tubes of coils.

Ceiling Diffuser

ceiling mounted air supply devices with slots or vanes

Roof ventilators

centrifugal exhaust fans suitable for outdoor installation.

Electronic and Pneumatic controls

control uses the receiver controllers to constantly adjust output air pressure to actuators in response to input pressures from sensors to produce desired result. Require manual calibration and adjustment.

Fan terminal units

designed to overcome several of the complaints about the performance of VAV terminals (stuffiness, etc.) - contains a VAV damper that responds to the space thermostat. Chilled air passing through the VAV damper is mixed with return air from above the ceiling and delivered to the space via a small constant-volume fan within the unit. - pressure requirements are low, and energy consumption is accordingly modest. - can also be equipped with heating coils and are sometimes used in combination with VAV systems.

controller

determines: - if signal goes to monitoring station or actuator. - If input/output signal is two positioned or proportional. - if input/output is direct or reverse acting.

Humidistats

devices that sense and respond to humidity-either relative or absolute. Sends signal to controller to decide where to add humidity through humidifier, or remove humidity by over cooling the air to remove excess air, and then reheated to desired temp.

Centrifugal Fans

draw air into the center of a rotating wheel. Vanes on the wheel project the air radially and tangentially toward the outside of the fan housing, which directs the air to the fan discharge. - can be freestanding or housed within cabinets or air-handling units. - used when saving space and simplicity of installation are important considerations. - The design of the blade affects its performance. Small ______________ most often use a forward-curved configuration. Backward-inclined blades are common on larger _____________, and blades can be constructed with an efficient airfoil shape rather than uniform thickness.

Two pipe system

each unit fed by individual supply branch each unit can be controlled flow rates are balanced

Most common applications of VFDs

found in the pumps and fans used for HVAC systems such as chiller-condenser water pumps, domestic-water booster pumps, air-handling fans, and cooling tower fans

AIR HANDLING UNIT FANS

generally centrifugal, although axial fans are occasionally used - The supply fan section of the air-handling unit can be placed in the draw-through or blow-through position with respect to the coils.

Ductwork

includes supply, return, outside air, relief air, and exhaust ducts. - fabricated from sheet metal (galvanized steel, aluminum, stainless steel, and can even sometimes be plastic or fabric

Balance Valves

installed to adjust the flow through the system in proper amounts to serve loads. These valves need to be adjusted when a building is commissioned and readjusted periodically as needs change. With "memory stops" to restore a set position, they can also be used as shutoff valves, reducing the number of components required and the expense of construction.

Shutoff valves

installed to isolate components and portions of systems. These valves avoid the inconvenience of draining and refilling entire systems or portions of systems during maintenance or repairs. If properly planned, they also allow continued service to portions of the system not affected by the work.

Control Valves

installed to modulate the flow of fluids through heat transfer devices in response to fluctuating loads. These valves are positioned automatically by actuators that receive input from control systems. Unlike shutoff and balance valves, control valves are in continuous operation. They are designed to wear well in movement and be accurate over a wide range of operatng conditions.

Duct liner

insulation applied to inside of ductwork. provides accoustical absorption, thermal benefits, and prevents condensation.

Dedicated Outside Air Systems (DOAS)

introduce 100 percent outside air and condition the air by introducing into air-handling units or directly into spaces. - Used in conjunction with fan coils or other terminal units which are not designed to provide ventilation. - capable of controlling the amount of outside air to a building or individual space to the minimum necessary for maintaining good air quality. Thus, saving energy.

actuator

manipulate equipment to meet desired set point of the controlled variable.

Sensors

measure monitored control variable.

Fan Performance

measured by: - Volume of air delivered per unit time (airflow rate), nor- mally in cfm - Pressure created (static, velocity, and total pressure), nor- mally in inches of water column (in. w.c.), inches of mer- cury column (in. Hg), or pounds per square inch (lb/sq in., or psi). (See Appendix C for conversion to SI units.) - Power input, horsepower (hp). - Mechanical and static efficiency, percentage. - Other factors, such as sound level in noise criteria (NC) or decibels (dB).

Proportional Signals

monitor and control variables that change continuously, such as temperature, pressure, or flow. Provide multiple levels of control and alarm through use of a single sensor or actuator.

Axial Fans

move air through their housings in a direction parallel to the wheel axle. -These types of fans can be used for general-purpose applications and have the advantage of being compact when installed in line with ductwork.

Control

occurs when a signal to the equipment causes the movement or adjustment of a component to produce desired result.

Single Zone system

one furnace controlled by one thermostat. Could be several rooms or even an entire building.

Equipment

selected predominantly to provide adequate capacity for the needs of the building under the design conditions

CV Dual Duct

send warm and chilled air through a pair of main trunk ducts to the areas being served. At the air-handling unit, a single fan blows air through a heating coil and a cooling coil into a warm-air trunk duct and a chilled-air trunk duct - capable of serving multiple zones - each zone served by individual mixing box - Mixing boxes are controlled with dampers to vary the quantity of warm and chilled air in response to the zone thermostat. - During warm weather, the cooling coil operates to provide air-conditioning, but the heating coil can be inactive, - cooling and heating can be activated simultaneously. - has no coils installed over occupied spaces;

Thermostats

sense and respond to. temperature, combining the functions of the sensor and controller.

CV Multizone

similar in operation to dual-duct systems. - Warm and cold air are mixed to produce the right air temperature for conditioning, according to signals from the zone thermostats - however, in these systems, unlike dual- duct systems, the mixing is done by dampers located at the air- handling unit rather than at terminals located near the spaces served. - can serve up to approximately 12 zones. - Like dual-duct systems, these systems waste energy because they mix warm and cold air. - disadvantage of being in- flexible with regard to change.

CV Terminal Reheat

similar in principle to single-zone reheat systems, except that multiple zones of temperature control can be achieved. - The air-handling unit contains a cooling coil that chills all the air supplied to the various zones. One or more main trunk ducts are used to distribute air throughout the area served, and a terminal box containing a reheat coil is in- stalled for each zone. The cooling coil chills air to the same temperature for all zones. The reheat coils respond to their respective thermostats to maintain temperature control in each zone. - capable of serving multiple zones from a single air handling unit. - flexible enough that one may add or rearrange reheat boxes on their main trunk as space is reconfigured. - poor energy use

Steam Distributing Steam Coil

steam is distributed evenly from an inner orifice tube within the outer heat- transfer tube. - ensures an even temperature across the face of the coil and is most effective in preventing freezing of the coil in below-freezing temperatures. - Steam distribution-type coil with tube-in-tube design. Steam is evenly distributed. - This type of steam coil is ideal for low-temperature preheating and special process applications.

General Purpose Steam Coil

supply (steam) and return (condensate) at different ends of the coil. - Coil temperature is likely to be lower at the far end of the coil, as steam is condensed inside the finned tubes.

Direct Return System

system where equipment closest to pump has the least pressure loss, and thus may have more or imbalanced water flow

VAV Reheat

terminals are equipped with electric or hot- water heating coils (see Fig. 3.20) and are similar to constant-volume reheat terminals except for control of the airflow (airflow is varied) - perimeter zones - When the space requires cooling, the VAV reheat terminal supplies chilled air. As the cooling load dimin- ishes, the amount of chilled air is reduced accordingly, to a preset minimum quantity. - When heating is required, the heating coil warms the minimum quantity of chilled air to a temperature that is suitable for heating the space. - Energy loss is much less than in constant volume reheating

Single Zone CV Reheat

used for air conditioning when humidity control is especially important. - Like the single-zone constant-volume system, this system is satisfactory only for single spaces with similar load characteristics or for large open spaces. - uses a cooling coil to cool and dehumidify air, along with a reheat coil for temperature control. Humidifiers may also be used - High Energy use - used only in special applications such as hospital operating rooms and computer rooms

Valves

used in Piping System to adjust and control the flow of the medium

Two Position Input system

used to indicate the operating status of the equipment, such as on/off, normal or alarm, open or closed. Start, stop, open, close, controlled equipment.

Utility Sets

weatherproof, single-inlet, generally roof-mounted centrifugal fans used in exhaust applications.