Down the Drain:
Energy Consumption at the Berkeley YMCA Pool
A Vital Signs Case Study
Prof. Alison Kwok/ARCH 507/University of Oregon Architecture Dept.
Methodology
Energy Smart Pools Info
Team Members:
Anne Deutsch
Ram Ganapathy
Geoff Grummon
Energy Smart Pools Info:
The software "Energy Smart Pools"is designed and maintained by
U.S. Department of Energy
Denver Regional Support Office
Design Team
Programmer: Janet Gunn
Calculations: Randy Jones, P.E.
Other Input: Al Hymer, Randy Martin, Brian Lawson
Aim:
The Energy Smart Pools program was developed to provide a reasonable, unbiased estimate of the energy savings and investment potential of pool efficiency/renewable energy options.
With a minimum of input data, the program can provide:
n A Base Case Energy Simulation of Annual Energy Costs
n Annual Costs, Savings and Payback of Adding a Pool Cover System
n Annual Costs, Savings and Payback of Adding a Solar Heating System
Base Factors:
All calculations are based on
1. Pool evaporation rate research
2. Standard engineering principles
3. Statistically compiled weather data, and
4. User input parameters reflecting operating conditions and schedules.
Assumptions for Base Pool energy Consumption:
- Energy use is due to pool evaporation losses and the requirement for outside air to control humidity. Convection, conduction and radiation losses are negligible.
- The program calculates evaporation rates and outside air requirements for three, eight - hour time periods each month. Average air speed at the pool surface is very low, about 10 feet per minute.
- Since it is assumed that swimmers are in the pool at all hours the pool is open, an high activity level is applied to the calculations and the factor for a "high" activity level is 1.7 is considered. These factors are based on recent experimental findings at Colorado State University.
- An average of the active (activity factor applied) and quiet pool evaporation rates is determined for each time period on the basis of the weighted number of hours the pool is open (operating) and closed (non-operating). Evaporation losses are converted to energy consumption at the rate of 1050 BTU/lb. This is around the latent heat of vaporization for water at 75 to 80 degrees F.
- The energy required to condition ventilation air is based on the theoretical volume of outside air required to remove evaporated water from the pool for each time period. (From the ASHRAE 1991 Applications Handbook)
- The maximum ventilation rate is limited to 4 cfm/sq. ft. of pool area. This "rule of thumb" constraint was chosen because it is simple to calculate and it should in most cases exceed required design rates. Note that ANSI/ASHRAE Standard 62-1989, "Ventilation for Acceptable Indoor Air Quality" specifies a minimum of .5 cfm per square foot of pool and deck area, and ASHRAE 1991 Applications Handbook recommends 4 to 8 air changes per hour for humidity control.
- Only energy to heat ventilation air from Sept. 15 to May 15 is considered. Cooling energy required in the summer season is not considered. A pool air conditioned in the summer will require more energy and realize more pool cover savings than that shown in the program.
- Ventilation fan and pump motor energy use and savings are based on user supplied values of motor hp, load, efficiency and run times. it is probably best to assume the load is 70% - 120% of motor rating, and the efficiency is in the 70%-90% range.
- Pump and fan performance efficiencies are not considered.
- Bin temperatures, mean coincident wet bulb temperatures, monthly wind speeds, percent sunshine, and barometric pressures are mostly from ASHRAE format weather files used in the building energy analysis program, ASEAM.
- Solar insolation data is from the ASHRAE 1982 Applications Handbook, Table of Total Irradiation on Horizontal and South Facing Surfaces Tilted at Various Angles on the 21st Day of Each Month.
Assumptions for Pool Cover:
- The pool cover is assumed to eliminate evaporation for the percent of pool area covered. This is specified by the user. The pool cover is assumed to be on the pool during all non-operating hours.
- A pool cover may also allow the pool owner to reduce the run time of the ventilation system because less humidity control may be required.
Assumptions for Solar heating System:
The program calculates savings for either a single glazed collector system or an unglazed system. The unglazed terminology is meant to include unglazed collectors made of black plastic or EPDM which can be a flexible mat or fixed panel design. The systems should be viewed as representative examples of the technology, but there are many other possibilities. Different collectors, storage systems, levels of freeze protection, features, and sizes are available.
The simplified analysis is based on
Collector efficiency (slope & intercept),
Monthly clear day total irradiation (not including reflected radiation),
Weather file percent sunshine, and
A clearness factor.
Other Related Assumptions:
- All collected thermal energy is used directly, without intermediate
storage. Collector efficiencies may be varied.
- For summer only pools, (opening and closing bounded by April - September) the system is assumed to face direct south at an angle to horizontal of latitude minus 10 degrees. For pools open longer than this or all year, the system is assumed to face direct south at an angle to horizontal equal to latitude.
- The program calculates pool loads and solar heating system output on a monthly basis.
- Generally it is desirable to size a system so that it will meet only part of the thermal load, so that all collected energy is used. The user specifies the size of the system.
Basic calculation Methods:
The following formulae and calculations and assumption factors are used for the output.
Evaporation Rates - Quiet Pool
Where:
Wp = evaporation rate of water, lb/hr.
A1 = area of pool surface, ft2.
C2 = 69.4 BTU/(hr-ft2)-in.Hg.
C = 30.8 BTU/(hr-ft2)-in.Hg.
u = air velocity over water surface, MPH.
Y = latent heat required to change water vapor at surface water temperature, BTU/lb.
Pw = saturation pressure at room air dewpoint, in.Hg.
P= saturation vapor pressure taken at the surface water temperature, in.Hg.
Evaporation Rates - Active Pool
Where:
Wq = evaporation rate of water for an active pool, lb/hr.
W = evaporation rate of water, lb/hr.
AF = Activity Factor:
Indoor Pool, Low Activity = 1.3
Indoor Pool, High Activity = 1.7
Evaporation Rates with a Pool Cover On
Where:
Wq = evaporation rate of water with cover, lb/hr.
W = evaporation rate of water, lb/hr.
Cover% = percentage of pool that is covered.
Annual Total System Energy Usage
Where:
Qta = annual total pool heating system energy use BTU/yr.
Q = annual total energy load, BTU/yr.
h = annual system fuel use efficiency, BTU/lb.
Active Solar Heating System Contribution to Pool Heating
Daily Insolation Values - I come from:
ASHRAE Tables - daily insolation (21st day of each month).
Surface Tilt = angle equal to location latitude for pools operated year round or before/after April - September.
Surface Tilt = angle equal to location latitude minus 10 degrees for pools operated only
( operated only) within the April - September time period.
Calculation of Average Hourly Insolation Falling on Collector Each Month - I :
Where:
Icd = BTU/ft2-hr.
Isun = BTU/ft2-day.
Hr = average number of hours the sun is up each day of that month.
Monthly Solar Energy Available from the System:
Where:
QsSOL = monthly solar load energy available from system, BTU/month.
Ys = Y-intercept of solar collector SRCC efficiency curve.
Mp = slope of solar collector SRCC efficiency curve.
Tdbs = pool water temperature, °F.
Tch = air dry bulb temperature for the 8:00am to 4:00pm time bin, °F.
Icd = average hourly insolation falling on collector, BTU/ft2-hr.
I = average daily insolation falling on collector, BTU/ft2-hr.
CpL = clearness factor.
Sc = mean percentage of possible sun which occurs in a given month.
A = surface area of solar collector, ft2.
Motor Electrical Fuel Use
Where:
F = motor electrical fuel use, kWh.
HP = motor horsepower, hp.
L = motor load factor.
HRS = hours of operation, hrs/day.
h = efficiency of motor.
Volume Flow Rate of Outside Air Required to Remove Evaporated Water for the Time Bin
Where:
V = quantity of air, cfm.
W4 = evaporation rate of water. lb/hr.
C = time conversion to minutes, 60 min/hr.
r1 = calculated air density, lb/ft3.
wo = humidity ratio of outdoor air at design criteria lb/lb.
w = humidity ratio of pool air at design criteria, lb/lb.
Hourly Energy Load for Outside Air for the Time Period
Where:
Qo = hourly air heating energy load, BTU/hr.
Vi = quantity of air, cfm.
To = indoor air temperature, °F.
Tb = outdoor air temperature, °F.
P = barometric pressure, in.Hg.
Data Inputs:
Type of Pool: Indoor or Outdoor.
Weather Site: State, and the city that most closely resembles berkeley’s weather.
Wind Speed %:
No windbreak: 30%
Moderate windbreak: 20%
Good windbreak: 10%
If in doubt, a figure of 15% can be used.
Shading %: Calculation assumes that the pool is completely unshaded during the peak solar hours of 8 am and 4 pm. Pools that are screened-in should use a shading percentage between 50-75%.
Open Date: Month and Day pool normally opens for the season.
Close Date: Month and Day pool normally closes for the season.
Hours/Week Use: Average hours per week that the pool is used or at least would be uncovered during each time period.
Open & Closing Times: The normal opening and closing times for each day of the week.
Pool Area: Includes the entire surface area in square feet.
Pool Temp (F): The normal temperature of the pool in degrees Fahrenheit.
Activity Level: Either high or low for normal activity level during open hours. Low indicates an average of up to 2 swimmers in a 1000 square foot pool over all hours of operation. High is any number over that.
Fuel Costs & Eff: Each heating fuel should have its own cost/unit entered based on local utility prices. Each fuel can have a default heating efficiency. This efficiency is based on an annual system efficiency and not the combustion efficiency.
Fuel: Type of heating fuel used to heat the pool.
Fuel Cost: Cost/unit of selected heating fuel obtained from past utility bills or from the local utility.
Pool Heater Eff %: Annual system efficiency and not the combustion efficiency. Based on manufacturers’ data and/or an assessment of how efficiently the heat delivery system operates.
Pump Motor HP: The horse power indicated on the pool pump.
Pump Motor Eff %: The estimated efficiency for the pool pump, generally 70-90%.
Pump Run Hrs/Day: The hours per day that the pump normally runs.
Pump Mtr Load %: The estimated % of load that the motor is running under. Properly sized motors generally operate at 70-100% of rated HP.
Room Temp(F): The normal temperature of the indoor pool room in degrees Fahrenheit.
Room Humidity %: The average relative humidity in the pool room.
Fuel: Type of heating fuel used to heat the indoor pool room.
Vent Heater Eff %: Annual system efficiency and not the combustion efficiency. Based on manufacturers data and/or an assessment of how efficiently the heat delivery system operates..
Vent Motor HP: The horse power indicated on the ventilation motor.
Vent Motor Eff %: The estimated efficiency for the ventilation motor, generally 70-90%.
Vent Run Hrs/Day: The hours per day that the ventilation motor normally runs.
Vent Mtr Load %: The estimated % of load that the ventilation motor is running under. Properly sized motors generally operate at 70-100% of rated HP.
Pool Cover Defaults: Default values for R-values and costs per square foot (system cost) for manual and automatic, bubble/solar covers, vinyl covers and insulated covers. Bubble/solar covers are similar to bubble packing material. Vinyl covers are heavier duty sheet covers. Insulated covers have an insulation material sandwiched between two layers of vinyl or plastic. The following lists typical R-values and costs:
Cover Type R-value $/sqft manual $/sqft auto
Bubble/Solar 1.5 $1.00 NA
Vinyl .10 $1.50 $6.00
Insulated 2.0 $2.00 $7.00
Cover Type: Either Bubble/Solar (like packaging material), Vinyl (any sheet type cover), or Insulated (insulation material is sandwiched between two layers of plastic or vinyl.
System: The planned system will be automatic or manual.
Cover R-Value: The estimated R-value of the pool cover.
Coverage %: If the pool can not be completely covered, then the percentage that is covered.
Installed Cost: The installed cost will be automatically calculated from the pool area and the default cover cost/square foot
Water $/1000 Gal: The cost per 1000 gallons that the local water department charges for water.
Pump Mtr Hrs/day: 24 hours per day.
Vent Mtr Hrs/day: The hours of ventilation motor operation can often be reduced when we add a pool cover. A value of 50% is a good place to start.
Solar System Defaults: Default values for solar collector costs per square foot and efficiencies. The Y-intercept and slope identify the collector’s efficiency curve. The higher the Y-intercept and the flatter the slope the more efficient the collector is. These values can be obtained from the manufacturer. All legitimate solar collectors have been tested and rated by the Solar Rating and Certification Corporation (SRCC). If in doubt, use $8/sqft for unglazed collectors and $30/sqft for glazed collectors.
Sqft Collector/Pool Area: A percentage of the pool area to be used for solar collector square footage.A value between 50-100%.
Collector Sqft: This number will be calculated based on the pool area and the default Sqft Collector/Pool Area percent.
Collector Type: Either unglazed or glazed collectors systems.
Eff Y-Intercept: The Y-intercept identifies the collector’s efficiency at a given outside temperature. The higher the Y-intercept the more efficient the collector is. These values can be obtained from the manufacturer. All legitimate solar collectors have been tested and rated by the Solar Rating and Certification Corporation (SRCC).
Efficiency Slope: The slope of the collector curve indicates the collector efficiency as it relates to outside temperature. The greater the downward slope the less efficient the collector at cooler outdoor temperatures. Unglazed systems usually have steep slopes, but are usually operated in warm temperatures. Glazed collectors have flatter slopes and can maintain a fair operating efficiency even at cold outdoor temperatures.
Installed Cost: The installed cost will be calculated from the pool area and the default collector cost/square foot.
Data Analysis& Output:
Base Pool Energy and water costs of pool w/o cover or solar.
Pool Cover Energy and water savings of using a pool cover.
Solar Heating Energy and water savings of using a solar pool heating system.
Cover and Solar The combined energy and water savings of adding both a pool cover and a solar pool heating system.
Conclusions:
The conclusions are based on the result reports from the software that includes monthly Btu consumption and savings with breakouts for evaporation, outside ventilation air ,radiation, convection, solar gains, solar heating system outputs and system summaries.