# HVAC

## Questions & Answers

1. Each of the windows in the Office has dimensions of 42 in. width and 60 in. height. What is the total area of the windows in ft² in the Office. 2. Each of the windows in the Dance Hall has dimensions of 54 in. width and 72 in. height. What is the total area of the windows in ft² in the Dance Hall. 3. What is the gross area of the outside walls in ft² for the Office? 4. What is the net area of the outside walls in ft² for the Office? 5. What is the gross area of the outside walls in ft2 for the Dance Hall? 6. What is the net area of the outside walls in ft² for the Dance Hall? 7. Use the crack method to determine the infiltration rate in CFM for windows in the Office. The windows are double hung windows. The infiltration through windows per foot of sash crack is 0.37 CFM. 8. Use the air change method to determine the infiltration rate for the Dance Hall. The air change rate per hour (ACH) is 1.5. Note: Round off the calculated to the tenths (first decimal place). 9. Using the infiltration rates calculated in problems 7 and 8 above, calculate the heat loads due to the infiltration in the Office and the Dance Hall. Note: Round off the calculated to the ones place (no decimal place). 10 Calculate the overall heat transfer coefficient, U in Btu/h ft2 °F, of the walls in the building. The construction of the walls is as below. Include inside and outside air films where appropriate. 11. Calculate the heat transfer rates in Btu/hr for the outside walls and windows in the Office. The windows are double glass aluminum frame window with 3/8 in. air space.

Your task is to devise a system that is able to accomplish the desired cooling requirements. The project can be divided into several steps: 1- Load estimation (lights, people, equipment, transmission through walls and roof...): discuss variation throughout the day and critical months of the year 2- Quantity and state of cooling air to be distributed through the main duct. 3- Duct and fan (optional) Sizing 4- Refrigeration System Design: this system uses refrigerant (R290) as the working fluid and could be a simple vapour compression cycle. The main constraint about this system is that it has to provide the cooling load calculated in part 1 but for 10 classrooms located on one floor of the school. Take assumptions when necessary and clearly state and justify taken assumptions in any of the design stages.

Moist air exists under conditions of 24°C db temperature and relative humidity 50 percent. The pressure is 101.3 kPa. Using the psychrometric chart, determine (i) the wet-bulb temperature, (ii) the dew-point, (iii) the humidity ratio, (iv) the enthalpy, and (v) the specific volume. Please show all the steps on the psychrometric chart.

The dry-bulb temperature and wet-bulb temperature of a sample of air are 30°C and 23°C respectively. The pressure of the air is 98 kPa. Calculate (i) the humidity ratio if the air is adiabatically saturated, (ii) the humidity ratio of the air, (iii) the partial pressure of water vapor and dry air in the sample, and (iv) the relative humidity.

Q2: The dimensions of room are 10-m by 6-m by 3-m high. The pressure, temperature and degree of saturation of the air in the room are 100 kPa, 25°C and 55 percent respectively. (i) Calculate the mass of air in the room. (ii) If the surface temperature of a window of the room is 10.5°C, will moisture condense out of the air?

Prove that the specific volume of the moisture air (v) can be estimated from the following equation: Where w to refers to the humidity ratio of the air, in kg/kg dry air.

1-Introduction 2-Use program - HAP in the design of systems and devices 3 Use program - HAP in estimating your cost and energy cost SHAP 4.6- Program Description Chapter 3: Data on the establishment of the air conditioning system 1-List General 2-list System Components 3-... Zone Components 4- Sizing Data 5- Equipment 6-System account reports

Moist air at 24°C, 1 atm, and 35% relative humidity enters an evaporative cooling unit operatingat steady state consisting of a heating section followed by a soaked pad evaporative cooleroperating adiabatically. The air passing through the heating section is heated to 45°C. Next, theair passes through a soaked pad exiting with 50% relative humidity. A. Determine the specific humidity of the entering moist air (to the heating section)_ B. Determine the rate of heat transfer to the moist air passing through the heating section, in kJper kg of the entering mixture. (20 of 45 points. Please input your final answer in the box below) C. Determine the specific humidity at the exit of the evaporative cooling section. D. Determine the temperature, in °C at the exit of the evaporative cooling section. (.

1. Consider water flowing to three faucets in a building through the very simple plumbing network shown below. Every section of pipe in the figure is 25 ft long. All of the piping is nominal half-inch type L copper piping. The inlet pressure to the main pipe is constant at 50psi and the pressure of the water leaving each faucet is 0 psi. The water has a temperature of 140°F. For the purposes of this analysis assume that there are no pressure losses in the fittings (elbows, tees, etc.) and that the only pressure losses are given by the following equation. \Delta P=f\left(\frac{L}{D}\right)\left(\frac{\rho V^{2}}{2}\right) Where f = 0.02, L is the length of pipe, D is the pipe diameter, V is the water velocity, and is the water density. What is the water flow rate in gallons per minute from each faucet A, B,and C?

Air at 95°F, 1 atm, and 10% relative humidity enters an evaporative cooler operating at steady state. The volumetric flow rate of the incoming air is 1765 ft3/min. Liquid water at 68°F enters the cooler and fully evaporates. Moist air exits the cooler at 70°F, 1 atm. There is no significant heat transfer between the device and its surroundings and kinetic and potential energy effects can be neglected. A. Determine the mass flow rate of the dry air in Ibm(dry air)/min. B. Determine the mass flow rate at which liquid enters in Ibm(water)/min.. C. Determine the mass flow rate of the moist air at the inlet. D. Determine the relative humidity at the exit.

A horizontal photovoltaic (PV) collector absorbs solar radiation and produces electricity.While 10% of the solar power is converted to electricity, the remaining 90% is lost to the atmosphere by natural convection to the ambient air and radiation to the sky. The sky has an effective temperature of 270 K and the ambient air has a temperature of 310 K. The PV has an emissivity of 0.9. The natural convection from the PV surface is given by the following equation. \frac{h L}{k}=0.15 R a^{0.33} R a=\frac{g\left(T_{P V}-T_{a i r}\right) L^{3}}{v^{2} T_{a i r}} P r Where g is the acceleration of gravity, L is the length of the PV array (L = 25 ft), v is the kinematic viscosity of air, k is the thermal conductivity of air, and Pr is the Pr and tl number. a. What is the temperature of the PV surface if the collector absorbs 1000 W/m² of surface area? b. Develop a plot of PV temperature as the absorbed solar radiation varies from 100W/m² to 1000 W/m².

Consider a cold day in Nederland, CO (elevation 8234 ft above sea level) with an atmospheric pressure 10.8 psia. If the temperature of the air is -10°F with a relative humidity of 50%, what is the dew point temperature of the air?

11.9 A duct system has branch sections to threetdifferent zones as shown in Problem 11.9 Figure. The volume flow rate and duct lengths are shown on the figure. The ducts are circular with right angle tees, diffusers with a loss coefficient of 0.2, and a sum of the loss coefficients for the fittings in each section of22. Assume a friction factor of 0.018 for each section and standard temperature and pressure.Determine the duct die a. Determine the duct diameters and pressure drops using the equal friction method. b. Determine the pressure in each zone. Using the generalized fan curve of Figure11.10, select a fan, and determine the fanpower required. d. Determine the fan power required for the same system when the total flow is reduced to 20,000 cfm with the same proportion of the flow to each zone and a variable speed fan employed. e. Draw some conclusions from your results.