Reference no: EM13703983

1. A) Calculate the heat loss rate at -10 F outside temperature, 70 F inside, assuming NO internal heat generation, i.e. shutdown at night.

B) Calculate the outside "balance temperature" when the building is fully lighted and occupied with 200 customers and employees.

C) The building is open and in operation 12 hours each day, and is shut down and essentially unoccupied for 12 hours each day, during the cold night time hours. Assume that there are 4000 deg.-F days of heating during these night-time hours. What is the annual heating bill (night-time) if natural gas is used (90% efficiency), costing $7 per 1000 cubic feet (approx. $7 per million Btu)?

D) Assume that you can cool the building adequately with outside air, if the outside air is below 15 C (59 F). Above that temperature, it is necessary to turn on the vapor-compression air cooling, which has a coefficient of performance of 4.00.

Estimate the electrical bill to provide the necessary air conditioning (air cooling) for a year. Assume that there are an average of 100 customers and employees in the store during the day, and that all the lights are on while the store is open for business, 12 hours per day. No A.c. is needed when the building is shutdown at night.

E) What is the total electrical bill for a year, lights, plus air condition, plus ventilating fans (to provide the required 15 cfm per person in the building? (The ventilation fans will use about 2.5 kW of electricity, and will only be needed during the 12 hours each day that the store is open.)

2. A movie theater owner is concerned about complying with ASHRAE standard #62 on air quality. It is a theater complex, each theater having a capacity of 200 people. Thus the ventilating fans need to be designed for nominally 3000 cfm, of fresh air. (Note, these could be variable speed fans, so the speed can be adjusted to the number of occupants, but let's assume these are constant 3000 cfm. )

A typical movie is two hours long, and has 100 patrons, each paying $6. If the outside temperature is 20 F, how much is it costing to heat this fresh air for the two hours? (The natural gas heat is costing $8 per mission Btu.)What fraction is this of the gross receipts?

3. Is a south facing window cost-effective in a home in Southeast Idaho? Assume no overhang (for sun shielding in the summer).

A) Consider only winter net energy loss or gain (from solar). Do the calculation for October through April, for Pocatello typical weather and solar radiation conditions.

B) Make a rough estimate of what you think the penalty of this window is for air conditioning. In general AC is only needed in July and August, the rest of the year can be handled by ventilation. Assume a COP of 3.0 for the AC system, and electricity cost of 5 cents per kWh.

4. Problems Involving the Psychrometric Chart. Consider a warm summer day in Idaho, dry bulb temperature 90 F, and reported relative humidity of 20%.

A) What is the wet bulb temperature? (This is the temperature your skin feels if there is a reasonable movement of air past the skin.)

B) That night it cools down. Assume that the water vapor content in the air remains constant as the cooling occurs. At what temperature will dew start to form?

5. Making sure your A.C. unit has a drain. A home air conditioner/air handler circulates 1400 cfm. The indoor air is nominally 77 F and 50% relative humidity. The air leaving, after passing over the refrigerant coils, is at 50 F and may be considered saturated. How many gallons of water per hour will drip from these coils?

6. Do the same problem for a warm day in Alabama, 90F and reported relative humidity of 70%.