HVAC PE Study

16 oz = 1 lb

1 Hz = 60 RPM

1 rad/s / 2pi = 1 Hz

$t_{eq}=r_{2}ln(\frac{r_{2}}{r_{1}})$

${total~yearly~energy}/{building~area}$

${total~yearly~energy~cost}/{building~area}$

Equate two figures into the same time period (e.g. annual) and solve for interest rate by looking up value on interest tables

Northern hemisphere:
south-facing: receive more sunlight in the winter
west-facing: receive more sunlight in afternoon during summer;
east-facing: receive more morning sunlight;
north facing: receive minimal sunlight year-round

power produced by pump/fan; amount of power required to meet needs of the system

power output of motor to turn on pump or fan; $BHP=\frac{MHP}{\eta_{mech}\%}$

size of the motor

standard size above BHP

electrical input required to turn on the motor and overcome friction losses

Electricity that can do actual work

Used to find real power; $S_{supplied~to~motor~(VA)}=\frac{P~[W]}{pf}$

$\frac{Brake~HP}{\eta_{motor}\%}=\frac{{Mechanical~HP}}{\eta_{motor}\%*\eta_{mech}\%}$

1. Evaporator: low pressure, low temp liquid/vapor mixture → absorbs heat → low pressure, high temp gas; 2. Compressor: low pressure, high temp gas → compressed high pressure, high temp gas; 3. Condenser: high pressure, high temp gas → high pressure, low temp liquid; 4: Expansion device: high pressure, low temp liquid → low pressure, low temp liquid/vapor mixture

warm air/water used to evaporate all liquid parts of mixture into saturated vapor; isobaric and ideally isothermal; cool water to chilled water that is distributed to air handlers

raises temperature of gas above temperature of fluid in condenser; ideally isentropic but some enthalpy change due to not being 100% efficient

$Compresser~Efficiency~(\%)=\frac{h_{2,ideal}-h_{1}}{h_{2,actual}-h_{1}}$

cold air.water used to remove heat from gas and condense it to liquid; reject heat to a heat sink via air cooling (fans blow air over condenser) or water cooling (piping to cooling tower)

X degrees beyond the saturation temperature. Evaporator superheats gaseous refrigerant.

reduces pressure of liquid adiabatically, where some is turned to gas

Energy efficiency ratio, measures practical efficiency of cycle; $EER=3.412*COP$

Integrated part load value; kW/ton metric given at various % load at standard AHRI conditions

Non-standard part load value; same as IPLV but adjusted to account for design (non-standard) conditions

two shells, refrigerant (water) + absorber (lithium-bromide/ammonia), heat source (hot water/steam, typically used with waste heat)

COP=evaporator energy (Btuh)/Heat in (Btuh), typically 1.5

constant entropy; ideal compressors

constant enthalpy; heat does not enter/leave system; dehumidifiers, evaporative coolers, expansion valves, throttling valve

constant temperature

constant pressure

$Q=\dot{m}\Delta h$ or $q=mC_{p}\Delta T$

$SHR=\frac{{Sensible~Heat}}{Total~Heat}$, i.e. slope of line on the protractor

$h_{gf}=h_{g}-h_{f}$; energy to vaporize liquid to gas

$T_{mix,db}=T_{1,db}*\%_{1}+T_{2,db}*\%_{2}=\frac{{T_{1,db}*CFM_{1}+T_{2,db}*CFM_{2}}}{CFM_{1}+CFM_{2}}$

Dry bulb temperature, humidity ratio, or enthalpy. NOT wet bulb temperature

Horizontally left from point until you hit saturation curve. NOT the same as wet bulb temperature.

sensible heating, decrease in RH; heating coils

sensible cooling, increase in RH; cooling coils

latent heating, humidification; steam humidifier

latent cooling, dehumidification

Use the slope obtained from the nomograph on the psych chart

downward diagonal movement depending on temperature of desiccant; possibly adiabatic

Heating dessicant to retransfer moisture into air

Can be sprayed with water solution over humid air to dehumidify; Li-Cl has high affinity for water
a) higher concentration of Li-Cl absorbs more moisture and vice versa
b) lower temperature can absorb more moisture and vice versa

Blow dry air over water or through water droplets
upward diagonal to left; essentially adiabatic since enthalpy lost be sensible cooling is gained by latent heating

in the handbook. only use DF or corrected air density, not both.

$Q_{steam}=\dot{m}*h_{fg}$

per thickness, can be per inch $[\frac{Btu-in}{{hr*ft^2*^\circ}F}]$ or per ft $[\frac{Btu}{{hr*ft*^\circ}F}]$

the reciprocal of conductive heat transfer coefficient, k (includes thickness); $\frac{{hr*ft^2}*^{\circ}F}{Btu*in}$

sum of all resistances

reciprocal of all resistances summed

h, based on flow over surface; check handbook of h value of vertical, horizontal surfaces with/without wind

most efficient at emitting radiation and absorbing incident energy; emissivity = absorptivity = 1

always equal to 1 for any type of body

roof/walls: conduction/solar radiation
skylights/windows: conduction/solar radiation
ventilation/infiltration
lights
people
equipment

roofs/walls: conduction
skylights/windows: conduction
ventilation/infiltration

combined convective and radiative heat transfer coefficient for indoor and outdoor conditions to help find overall heat transfer coefficient; values in the handbook

Cooling Load Temperature Difference; used for heat transfer through roof and walls instead of change in temperature
Only used for cooling loads

depends on how the motor is configured relative to its respective equipment; equations in handbook

hooded appliances have only sensible heat load since all latent and convective loads removed; if hooded use radiation factor

$Convection~(T_{inside}-T_{surface})=Conduction~(T_{surface}-T_{ambient})$

temperature at which all air would be cooled if the cooling coil was 100% effective. Must be on saturation curve

how much of air hits and is cooled by coil, percentage of air cooled to apparatus dew point; $Contact~factor=1-Bypass~Factor$

percent of air not cooled to ADP, function of airflow; $Bypass~Factor=\frac{{h_{leaving~coil}-h_{ADP}}}{h_{entering~coil}-h_{ADP}}=\frac{{T_{leaving~coil}-T_{ADP}}}{T_{entering~coil}-T_{ADP}}=\frac{{W_{leaving~coil}-W_{ADP}}}{W_{entering~coil}-W_{ADP}}$

account for fitting losses using k as a loss factor (found in handbook)

$x=\frac{{h-h_{f}}}{h_{g}-h_{f}}=\frac{m_{vapor}}{m_{vapor}+m_{liquid}}$ (in handbook)

Transfers heat from water to air via evaporative cooling (via a small portion of liquid being evaporated by an airstream) to cool water. Air enters dry and leaves higher in temperature and near saturation while water is cooled down to a lower dry bulb temperature.; $q_{cold~water}=q_{air}$

$Approach=T_{water,out}-T_{air,in,wb}$; describes performance of cooling tower, where the smaller the approach the closer to maximum possible heat transfer

$Range=T_{water,in}-T_{water,out}$;

$Effectiveness=\frac{Range}{Range+Approach}*100\%$

Equate water heat loss to heat gain through evaporation: $500*Q~[gpm]~*(T_{in}-T_{out})=500*evaporation~rate~\left[ \frac{gal}{min} \right]*H_{vp}~\left[ \frac{Btu}{lbm} \right]$

Amount of water carried out through airstream (~0.2%)

Draining of concentrated TDS then replacement with fresh water

move air through cooling tower using mechanical fans

move air based on difference in buoyancy of airstream inside and outside of cooling tower

fans located at exit of airstream and suck air into cooling tower

Fans blow into the cooling tower and located at airstream entrance

Counter-flow - air and water have directly opposing directions; cross-flow - air and water flow 90 degrees to each other

gross heat from combustion of fuel (Btu/lb or Btu/lb^3)

net heating value from combustion without latent heat of vaporization

$Q_{boiler}=\dot{m}_{fuel}*{HHV}*\eta_{boiler}$

Extract additional heat from flue gases to provide higher efficiencies by condensing moisture out of waste stream to provide additional heating

non-condensing; products of combustion contained within boiler tubes and water passed over tubes within a shell

non-condensing; products of combustion within shell and water kept within small tubes

Counterflow increases coil capacity and maximizes heat transfer

Number of transfer units method; used for when LMTD unkown:
1. calculate NTU
2. Find effectiveness based on NTU and heat capacity ratio $C_{r}$,
3. Calculate heat transfer rate: $Q_{actual}=Q_{max}*\epsilon$, $Q_{max}=C_{min}*(T_{hot,in}-T_{cold,in})$
4. Solve for remaining unknowns using $Q=mc_{p}\Delta T$

compressor is replaced with a generator/absorber and a heat source

Positive displacement:
Scroll - 10-400 tons
screw - 70-500 tons
rotary - 70-500 tons
reciprocal - 10-60 tons
Dynamic: centrifugal

compressing gas by squishing gas into an ever smaller volume

compressor and motor in a welded, airtight container; need to account for motor heat

compressor and refrigerant located in an enclosure while motor connected outside via a shaft

motor and compressor located in a mechanically sealed container that can be opened

refrigerant directly cools air

direct expansion system; split between condensing unit (compressor, condenser, expansion valve) and fan coil unit (evaporator and fan) where refrigerant flow varies to maintain temperature

Uses vapor compression cycle to heat instead of cool; condenser used to heat space and evaporator absorbs heat from exterior; heat source from ambient air, water, or ground

Double suction - fluid enters impeller on both sides
end suction - suction and discharge 90 degrees to each other
in-line - suction and discharge in-line
split-case - number of stages fluid proceeds through
centrifugal - conversion of rotational kinetic energy to produce a flow rate

Axial - fan shaft with fan blades attached around the shaft
Centrifugal - fan wheel with blades (impellers) along the circumference of the wheel. Air enters center where centrifugal force due to spinning of the fan wheel causes increase in air speed that creates a suction pressure at inlet of the fan wheel. Air then flows out the edges of the fan wheel and follows the fan housing to the air outlet

Propeller - propeller fan in housing
Tube-axial - propeller fan placed in tube; can handle higher pressure
Vane-axial - variation of tube-axial where inlet vanes provided to straighten air and increase efficiency

forward inclined, backward incline, backward incline airfoil, propeller

Unique to pump and given by manufacturer

based on piping system (pipes, fittings, valves, and equipment) that the pump will be connected to; static pressure translates curve up

intersection of system and pump curve

produce flow equal to the sum of the flow of each individual pump at every pressure point; move right along flow rate axis

sum pressures of each pump, while flow remains unchanged; move directly up the pressure axis

reduces flow by closing valve/damper, same power. Adds pressure to system

reduces flow by reducing frequency -> reducing RPM and power of motor. RPM changes so pump curve changes, parallel to old curve

1. Open system - $NPSHA=P_{abs} \pm P_{elev} - P_{fric} - P_{vapor}$
2. Closed system - $NPSHA=P_{gauge}+P_{velocity}-P_{vapor}$

1 psi = 2.31 ft/SG (in handbook)

$1 psi = \frac{144~\frac {in^2}{ft^2}}{62.4~\frac{lb}{ft^3}} = ft~head $

$h_{P_{velocity}}=\frac{v^2}{2g}~[ft~head]$

static pressure of a liquid reduces to below the liquid's vapor pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate shock waves that may damage machinery and piping

Should operate within the stable region, as within the unstable region a given pressure value can have multiple CFMs; less change in CFM per change in pressure in stable region

summation of all friction losses in the ducting system at varying CFMs; intersection of fan curve and resistance curve is operating point

1. Red curves show impeller diameters and pressure at varying flow rates
2. Intersection of red curve and blue horsepower curve show horsepower required at operating point
3. Intersection of red and green curve show efficiency at operating point

maintain a set pressure or flow

globe valve - consists of a plug and a seat, where the plug is raised/lowered to increase/decrease flow
ball valve - ball in center of valve can be turned to enlarge or shrink the opening; opening is perpendicular to direction of flow when valve closed
butterfly valve - disc in the center of the valve that can be swung open and closed

Relationship between flow rate and % open/close status of valve

flow rate through valve in one minute at 1 psi; $C_{v}=\frac{Q}{\sqrt{ \Delta P}}$

Equation valid only when change in pressure across valve much less than operating pressure:
$Q~[scfh]=59.64*C_{v}*P_{operating}\sqrt{ \frac{\Delta P}{P_{operating}} }\sqrt{ \frac{520}{SG*T} }$
scfh = standard cubic feet per hour
T = absolute temperature (Rankine)

point where flow rate does not change no matter %open/close of valve

control flow of air by modulating or two-position control, open/close

Determines controllability of the damper; lower the value the less control at higher percentages of max airflow

dividing pressure drop through damper when open by total pressure drop through ducting (only includes ducting affected by the damper)

Global warming potential; reference point is $CO_{2}=1$

Ozone depleting potential; reference point is CFC-11 = 1

HCs - hydrocarbons
CFCs - chlorofluorocarbons
HCFCs - hydrochlorofluorocarbons
HFCs - hydrofluorocarbons
HFOs - Hydrofluoroolefins

R-12,R-11; contains ozone depleting chlorine and high GWP; phased out in '95

R-22,R142B; containes ozone depleting chlorine, high GWP; phasing out

R-134a,410A,32; ODP=0 but high GWP

HFO-1234yf; ODP=0 and very low GWP; next gen refrigerants

Expansion valve, accumulator, filter, oil separator, hot gas bypass valve, receiver, filter/dryer, solenoid valve, sight glass

suction side of compressor after evaporator; accumulates excess liquid from evaporator that can damage compressor

placed at evaporator exit; prevents contaminants from entering the compressor

high pressure side of compressor - removes oil from refrigerant stream collected from oil seals/lubrication to ensure high heat transfer from refrigerant

controlled by compressor inlet temperature; if evaporator temperature too cold, hot gas bypass the condenser and sent to the evaporator to create a false load to prevent frost

after condensor; collects all the refrigerant liquid

before expansion valve; protects expansion valve by removing contaminants and water moisture that could freeze the expansion valve (expansion valve lowers pressure to turn refrigerant to gas, but could freeze water as well if present)

after filter/dryer and interlocked with compressor; shut-off and open flow through system; when compressor shuts off and solenoid valve closes, separation between high pressure (condenser) and low pressure (evaporator) side

close to expansion valve - diagnostic tool to see refrigerant quality entering the expansion valve; check if refrigerant is liquid or gas and if frost or moisture forming

air handling unit, supply ducting, dampers, terminal units, diffusers

- Use to convert rectangular ducting to equivalent circle diameter; equations in handbook
- Hydraulic diameter for flow
- Equivalent diameter for duct air flow

Fan with cooling/heating cools, where exhaust air is replaced with new outside air

(in order)
1. Mixing box - mixes correct amounts of outside air with return air using dampers
2. Air filter - protects following devices and keeps them clean
3. Heating and/or cooling coil - conditions air to correct leaving temperature
4. humidifer/dehumidifier - condition air to correct leaving humidity
5. Fan - provided ahead or behind devices depending on design; if last draw-thru, if first blow-thru
6. Energy recovery device - placed if applicable

controls amount and conditions of air distributed to specific space, e.g. VAVs

control the way air distributed throughout the space; maintain minimum air velocity

noise criteria, throw, velocity

Air diffusion performance index - statistical percentage of points when measured uniformly within space whose draft velocities and temperatures fall within comfort criteria; <80 acceptable

1-4-way signal how many directions you can throw the air out
numbers in column corresopnd to terminal velocities 150, 100, and 50 ft/min

- fans at AHU either on or off
- manual balancing dampers adjusted to supply a set airflow rate through diffuser based on max design conditions
- minimal controls for only one temperature zone

heating coil installed in-line with duct to provide sensible heating; only allowed in specific scenarios:
1. One constant volume AH serves multiple rooms with different cooling schedule, but only one space thermostat to control fan; use reheat for more control
2. Reheat coil used to add load to prevent overcooling

adds variable frequency drive (VFD) to fan in AHU and VAV boxes in supply air branches to adjust airflow based on cooling demands; reheat included if minimum airflow high enough

one duct supplies hot air and other supplies cold air; dual duct VAV boxes connect to both air supplies so can mix in varying proportions

- temperature sensor connect to VAV box controller and modulates damper to adjust cool air flow as needed
- when damper at min position, reheat has override; if open then damper has primary control
- pressure sensor ~2/3rds down the main duct branch to maintain system pressure and airflow rate
- track dampers used to verify sufficient outside air supply (or DOAS used)

$GPM*{\frac{1}{448.83}=ft^3}/s$

supports that restrict movement of pipe in all three dimensions

Equations found in handbook for calculating length of these bends to account for stresses

rejects heat to ambient air, so piping transports CHWS to air handlers/fan coils units; 3-way valves used to supply CHW to air handler or bypasses

rejects heat to water which is brought to cooling tower

variable speed pumps to distribute chilled water through a single loop between chiller and air handler

two chilled water loops; primary loop circulates CHW through the chiller, secondary loop circulates CHW to air handlers

supplies and returns CHW in the most direct path, where the first AHU to receive and return CHW is closest to the chiller and the last AHU is farthest from the chiller (pressure drop needs to be accounted for from start to end via balancing)

equalizes pressure throughout the loop by supplying the AHU closest to the chiller with CHW first, but the last unit to return

distributes both CHW and HW using different piping configurations (two pipe, four pipe, four pipe separate)

1.convert equipment Btuh value to cubic feet/hour of gas flow using either the HHV (if equipment is condensing) or LHV (if equipment not condensing) of fuel
2. find length of piping from delivery point to most remote outlet
3. Use natural gas pipe sizing table in handbook to get maximum CFH for each pipe size

1. convert equipment Btuh value to cubic feet/hour of gas flow using either the HHV (if equipment is condensing) or LHV (if equipment not condensing) of fuel
2. for each branch pipe section, take gas flow rate and the total length from that pipe section to the starting point (including length of pipe section too)
3. Use natural gas pipe sizing table in handbook to get maximum CFH for each pipe size

Use steam pressure drop through piping table in handbook

Efficiency = change in enthalpy between steam and feedbwater over input energy from fuel
$\epsilon_{boiler}=\frac{\dot{m}_{water}*(h_{steam}-h_{feedwater})}{\dot{m}_{fuel}*HHV}$

precool warm humid air by transferring heat to exiting cool supply air; typically used in warm humid climates in spaces with high outside air requirements

two heat exchange coils connected by piping, a fluid, and a pump; heat transfer fluid pumped between two coils to transfer heat from one air stream to another

two sets of dampers, where one controls the amount of return air directed either to exhaust or back to the AH and another set controls amount of outside air routed to AH

ratio of change in output signal to change in input signal

Slowly increase chilled water temperature as load conditions fall (based on return air or outside air)

Slowly increase supply air temperature if return air conditions or outside air conditions are met.

temperature setpoint modulated by control system to match load of the system

control system controls OA and RA dampers and an exhaust air fan on an AH to use less energy

Safety Standard for Refrigeration Systems - Lists allowable refrigerant quantities per room volume and other safety considerations; has safety groups for each refrigerant

$Q~[CFM]=100G^{0.5}$, where G=max lbs of refrigerant

Safety Class of Refrigerants - Lists refrigerant safety groups, concentration limits, other refrigerant info

occupational exposure limit - concentration of refrigerant a person can withstand for a certain amount of time (~15 minutes)

lower flammability limit - lowest concentration (density) of refrigerant in air that can ignite at certain temperature (140F) and pressure (atm)

Thermal Environment for Human Occupancy - Human comfort limits: draft, temperature, clothing

Ventilation for acceptable Indoor Quality - establishes minimum qualities of fresh air through different types of occupied space to limit recirculation

- Class 1 - low contaminant concentration (RA from offices, lobbies, libraries)
- Class 2 - moderate contaminant concentration (RA from art classrooms, nail salons, toilets, etc)
- Class 3 - significant contaminant concentration (RA from mechanical rooms, laundry rooms)
- Class 4 - highly objective fumes, dangerous particles, gases (RA from labs and chemical storage)

Ventilation for Indoor Air Quality in Low Rise Residential

Energy Standards for Buildings Except Low Rise Residential Buildings - minimum level of energy efficiency for HVAC systems and other building systems

Energy Standard for low rise residential

Standard for High-Performance Green Building, except Low Rise Residential - More stringent requirements than ASHRAE 90.1

Standard for the Installation of Air-Conditioning and Ventilating Systems - requirements for AC and ventilating equipment w.r.t fire protection

measure of smoke concentration of a material when it is burning; max allowed is 50

smoke damper required at all smoke barriers and should be activated automatically

how well a material burns and spreads a fire; maximum allowed is 25

fire dampers required at all fire rated walls or partitions of 2 hours or more

Standard for the Installation of Warm Air Heating and Air-Conditioning Systems - provides requirements for ducts, heating panels, boilers, etc.

Standards for Ventilation Control and Fire Protection for Commercial Cooking Operations

plan for phasing out ozone depleting substances like CFC's and HCFC's

Definedi n ASHRAE 62.1: $(min)~Fresh~air~flow~rate~(CFM)=R_{p}*(\#~of~people)+R_{A}*(Area)$
- R_P=people fresh air rate (CFM/person)
- R_A=area fresh air rate (CFM/Area)

minimum efficiency reporting value for air filters - MERV-6 minimum

properly isolate or dampen moving parts to avoid damaging equipment and supporting structures

1. Find disturbing vibration frequency (frequency the equipment is vibrating)
- fans, pumps, motors have frequency equal to their RPM (e.g. 1800 RPM * (1 min/60 s) = 30 hz)
- find and use lowest frequency if multiple, since it'll also isolate higher frequencies
2. Choose transmissibility of vibration isolator (amount of vibrations transmitted through isolation system)
$Isolation (\%)=100-Transmissibility (\%)$
3. Find natural frequency of vibration isolator required to achieve this transmissibility
4. Use required natural frequency to select vibration isolator
- consider support weight and deflection amount as well

The greater the ratio of $\frac{f_{d}}{f_{n}} > 1.4$, the greater the attenuation of transmissibility (decreases with square of frequency), i.e. vibration isolation improves

Use selection guide for vibration isolation table in handbook

HVAC equipment, air turbulence

"Heat source strength": $dB=10\log\left( \frac{W}{1*10^{-12}} \right)$

"Resulting temperature": $dB=20\log\left( \frac{x~Pa}{20*10^{-6}~Pa} \right)$

$Sound~Power=Sound~Pressure+10\log\left( \frac{4\pi r^2}{A_{0}} \right)$
r = distance away from equipment
A0 = reference area (typically 1 m^2 or 1 ft^2)

provide sound levels at range of frequencies

give sound levels at lower frequencies a lower rating since they're not as easily heard by the ear

$L_{A}=10*\log(10^{DBA_{1}/10}+10^{DBA_{2}/10}+\dots)$; can also be used to combined multiple sources of noise

Room or space must be lower than all points of a given NC curve to meet that NC rating

Use duct insertion loss table in handbook to calculate sound power loss over duct lengths

Sound reduces in proption to distance squared

primarily based on velocity; noise increases with turbulence and exacerbated by elbows, expansions, contractions that cause less smooth flow