Improving Energy Efficiency of Buildings

Why are we concerned with the energy efficiency of buildings?

Title 24 of the California Code of Regulations (also known as the Energy Efficiency Standards for Residential and Nonresidential Buildings) was implemented in 1978 to reduce California’s relatively high energy consumption at the time. Title 24 was later revised in 2016 to raise the minimum efficiency standards of buildings based on more modern efficiency technologies. In an attempt to meet these standards and eventually achieve zero net energy use, the city council of San Luis Obispo has expressed interest in retrofitting current public buildings to reduce the total amount of power required for their operation. The city highlighted their targets for reaching these goals of building efficiency in their Climate Action Plan. This project investigated four different retrofitting options and used three different public buildings as case studies. The goal of this project was to ultimately find ways of reducing wasted energy in the different buildings studied. Reducing energy waste is not only more economical for the city of San Luis Obispo, but also will allow the city to reduce its contribution to the production of greenhouse gases and overall global climate change.

What are the demographics of the community we are serving?

SLO is situated along the central coast of California, midway between Los Angeles and San Francisco. It is classified as climate zone 5 in California. Weather trends at the SLO County airport, provided by Weather Spark, were used to estimated the daily high and low temperatures throughout the year. Daily highs averaged between 65˚F and 78˚F and daily lows averaged between 40˚F and 55˚F. Cloud cover is also very low most of the year– little to no cloud cover around 92% of the time in the summer months. However, cloud cover becomes significant in the fall and winter months, with the skies clear only 54% of the time. With such moderate temperatures, many buildings in SLO do not require (and are often not equipped with) air conditioning, making the city council goal of zero net energy more attainable.

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Map of San Luis Obispo, courtesy of Google Maps

Population 46,400
Population density 3,500
Demographic Breakdown:
African American
Asian of Pacific Islander
Hispanic or Latino
Average Annual Median Income
(Family of 4, For California)
Average Annual Energy Consumption per Capita
(For California)
196 million BTUs

What specific buildings in SLO are we concerned with?

Using available public records, we looked at total building energy, building square footage, and building use. We found that Fire Station 2, despite being the smallest fire station, uses a large amount of energy compared to the other fire stations. Upon further investigation, we found Fire Station 2 is the oldest station in the city, being built in 1953. Because building practices have changed significantly since 1953, we decided to look into ways of retrofitting Fire Station 2 to update its efficiency. The Ludwick Community Center is a large public space that is occupied for programs and special events. Ludwick Center already takes advantage of some energy efficiency upgrades, namely, solar panels installed on the gymnasium roof and cool roofs implemented on their flat roof surfaces. We looked into ways to increase the energy efficiency of this building by updating the HVAC system, making further roofing changes, and insulating the walls. The parking structures in the city are also large consumers of energy. These buildings are open to the outside environment and do not have people working in them and therefore do not have central HVAC systems. Instead, the main energy consumption in the parking structures are lighting. A portion of the lights are on 24 hours a day, and all of the lights are on during hours of darkness. Being able to focus solely on lighting technologies made the parking structures a good place to improve efficiency.

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What are current solutions to the inefficiency problems we face?

Heating inefficiencies can be reduced by sealing buildings with expandable aerosol spray foam. However, the use of aerosol products produces chlorofluorocarbons, which are the major culprits responsible for hole’s in the Earth’s ozone layer. Our team is therefore investigating alternative, more sustainable approaches to sealing sites of heat loss in buildings.

Cooling (and heating) inefficiencies can also be mitigated by using more efficient HVAC systems: Heating, Ventilation, and Air Conditioning. Many of these buildings are using HVAC systems meeting the minimum SEER 13 standard (for more information on SEER/EER see here), while there are much more efficient systems being produced recently. Retrofitting these older buildings with newer systems has a large impact on their energy use and carbon emissions. Additionally, improving the solar reflectance of the roof (i.e. a cool roof) can decrease the indoor temperature and therefore the usage of cooling systems.

Lighting efficiency can be greatly improved with Smart Bilevel LED lights. These lights operate by emitting full light when motion is detected, and only 50% of their light when no motion is detected. Smart Bilevel LEDs are therefore attractive efficiency alternatives to compact fluorescent lights and even conventional LED lights.

Improving HVAC Efficiency in the Ludwick Community Center and Fire Station #2

In 2016 Lennox, the HVAC company, released a system with a large leap in SEER rating. Previously the highest rating was 21; Lennox’s new system is rated at 26 BTU/Wh. Compared to the currently installed systems with SEER of 13, the XC25 uses half the energy of the current systems to cool (heat) the same amount. At an estimate, from an article posted in August of 2016, the units cost $3850 and the installation costs $4000. The warranty on the system is 10 years, as listed on Lennox’s website.

A full informational sheet was not procurable, but the SEER rating tells us how much energy it takes to cool a certain amount. This means that, assuming the building’s cooling needs don’t suddenly change with the installation of the new unit, we can find a factor of energy efficiency improvement. This lets us easily calculate the energy use of the replacement XC25 unit given the energy use of the unit to be replaced.

Fire Station #2
For the Fire Station, the current unit was not listed in the building plans. To find the model number, we located it near the right side of the building (pictured below), and found the model number on the side using binoculars. Its document sheet is located here, but the relevant information is that the fire station utilized the 5-ton 4TWB3060A1 unit, which we estimate draws 4.7 kW while in use.

The spreadsheet made for the calculations of both the Fire Station and the Community Center will be uploaded at the end of the section, but we estimated the average running time per day of the HVAC was 8 hours. This can easily be converted to a number of kWh per year of electricity used, and from there the cost. Using these numbers, as well as a few other relevant ones such as price of electricity, number of units before and after the retrofit, SEER ratings, and the cost of the units, we can calculate savings (both in money and in emissions) and a simple payback period.

For the Fire Station, using the assumptions stated, we calculate a simple payback period of 5.45 years. This seems to make sense, since the unit is in so much use that doubling its efficiency would decrease electricity use dramatically. In fact, we estimate the retrofit would save 8,830 kWh of electricity every year.

All the numbers in the spreadsheet can be edited very easily, and most likely should be. Some of the assumptions that were made, due to difficulty of getting in contact with the city and not being officially affiliated with the city or the buildings for purposes of receiving accurate quotes, may be inaccurate. Even the amount of time the HVAC unit is running per day would require an entire study on its own, due to extra considerations such as leaving doors open while the unit is running and the fact that the unit is not running at full tilt whenever it is on. Also, the efficiency of the unit while heating is slightly different.

Extra investigation would be required to procure more accurate numbers, but the model itself is sound. Some suggestions are to assemble sensors from Arduinos to log how long doors are left open, as well as possibly wiring the HVAC unit to a power logger for an extended period of time to see exactly how much energy the unit uses.

Ludwick Community Center
The calculations for the Community Center are much the same as those for Fire Station 2. The building plans can be found below– the relevant page for this section of the project is page 19. From there we found information on the model numbers of the HVAC units listed, which can also be found below.
Ludwick Center Site Plans 102510.pdf Ludwick.pdf

However, the Community Center is slightly different than the Fire Station for a few reasons. One large difference is that the community center has 5 separate units in use. Another is that the Ludwick Center is only occupied while events are going on, so an estimate for the running time of the units is very difficult. Another difficulty is that the units are not all the same size– some are 5-ton units while others are 4-ton units. These were analyzed separately, but both sizes were replaced with the same 5-ton XC25 unit. Complicating things even more is that some units are dedicated to certain rooms such as the kitchen, which makes the running time even more difficult to estimate. Like the Fire Station, a more in-depth study would need to be done in order to find out exactly how much energy the current systems use.

Despite these complications and inaccuracies, the model still holds. Using the assumptions stated, savings were calculated in the same fashion. If the city were to replace the three 5-ton units in the Ludwick Center, they would save 17,884 kWh per year, which corresponds to a payback period of 8.07 years. Replacing the two 4-ton units would save the city 8,295 kWh per year, with a payback period of 11.60 years, which is over the warranty of
the system. However, provided the system lasts long enough, the money saved is still significant– especially after the unit is paid for.

All our calculations regarding the HVAC systems were made in the spreadsheet below. If this project is continued, all the numbers can be updated to more updated data.
HVAC City.xlsx

Improving Lighting Efficiencies for Parking Structure


Figure 1: 842 Palm Street Parking Structure at night

In our preliminary research, we found that the parking structures in the city of San Luis Obispo were large consumers of energy. Upon further study, we found that all lights on the interior of the parking structures were on all night, despite the lower occupancy.


Figure 2: Fully illuminated parking structure at night

For our study, we focused on the parking structure located at 842 Palm Street. We found that the parking structure currently uses HPS (high pressure sodium) bulbs for lighting. The current lighting system is controlled by a network of timers and sensors that are programmed to turn off some of the lights during the day in order to conserve energy. Our team conducted a site visit and saw approximately 108 lights in the structure. One third of those lights (36) were on during the day and all 108 were on at night.

Since much of the energy was being wasted at night on lighting non-occupied spaces, we researched energy saving lighting technologies. Light emitting diodes (LEDs) are the most obvious choice for energy savings, but at night there is such limited occupancy, we looked into occupancy sensing technology. True occupancy sensors (only illuminating when the space is occupied) were ruled out because of safety concerns associated with a completely dark public space. Our research led us to Bi-Level LED technology. Bi-Level LEDs consist of new, energy efficient LED lighting fixtures in conjunction with occupancy sensors. The fixtures and sensors can be programmed to have a lower level of light in the space at all times and illuminating brighter when occupancy is detected.
Further research led us to CREE Lighting products. CREE has been an industry leader in LED technology and uses Bi-Level LED technology in many of their fixtures. After contacting Neal Lighting & Controls (the local CREE Lighting Distributer) we were told the CREE IG Series and 304 Series would be most applicable to our project.

Table 1 contains information about the current HPS bulbs, a potential LED retrofit, the IG Series, and the 304 Series fixtures. The lumens, power consumption, and cost of each fixture is shown. The Bi-Level LED fixtures are programmable to provide between ≈10% and up to 100% power and lumens in the low illumination mode. For the purposes of this study, we assumed they were programmed to 50% power in the low mode and 100% power in high mode.

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Table 3: Cost, power, and lumens of lighting fixtures

Using this information, we calculated the amount of energy each lighting technology would use. We assumed that throughout the year, the parking structure would receive an average of 12 hours of daylight and 12 hours of darkness. We also assumed that during the night, the amount of time the Bi-Level LEDs were in the HIGH mode would be negligible when compared to the time they were in low mode. The results of these calculations are shown in Table 2.

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Table 4: Energy used by lighting fixtures in 842 Palm parking structure
*Fixtures on during daylight hours* *Fixtures on during night time hours

After the total yearly power consumption for each lighting technology was calculated, a simple financial analysis was performed. Figure 3 shows these results. We calculated the total cost of electricity per year using the San Luis Obispo energy price of $.15/kWh. The fixture cost was calculated by multiplying the cost per fixture by the 108 fixtures needed to outfit the building. The savings per year was calculated in comparison to the current HPS bulbs. The simple payback period was calculated by dividing the total fixture cost by the savings per year to determine how many years it would take to recover the capital costs by energy savings alone

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Table 5: Financial analysis of different lighting technologies
*Compared to current HPS lighting* *Without installation costs
The positive environmental impact (in terms of abated C02 emissions) and cost of conserved energy can be seen in table 6.

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Table 6: Energy and carbon savings
*Units=$/tonC02*year* *Units=$/kWh

All of the lighting technologies provide energy savings when compared to the current HPS fixtures. The LED retrofit provides the least energy savings, but also at the least cost. The IG series lights are the second lowest cost, but also provide the least amount of light. It is possible that more of the IG series fixtures would be needed to provide the same illumination as is currently in the parking structure. A further study of illumination needs should be conducted to see if these fixtures are viable. The 304 series provides significant energy savings, as well as comparable lumen output to the current HPS bulbs. The 304 series fixtures require significantly more initial capital investment.

It should be noted that installation costs are not included in this study. Accurate, quantitative data is difficult to obtain for installation costs, but qualitative results can be interpolated. The LED retrofit would have the lowest installation costs because the same fixtures could be used; the HPS bulb is simply replaced with a LED bulb. Both the 304 and IG series fixtures would require installation by a commercial electrician. Costs for the installation of both fixtures should be similar, but the 304 series is ten pounds heavier, which may result in slightly higher installation costs.

In addition to the energy savings provided by any of these light fixtures, they also help the City of San Luis Obispo achieve their CAP by reducing GHG emissions. By using less energy, the carbon released into the atmosphere through electricity generation will be abated. The cost of conserved energy for any of these technologies is also comparable to the cost of electricity in San Luis Obispo. That means that these technologies areeconomically feasible provided the funds to cover capital costs can be provided.
Calculation Spreadsheet for future use:PHYS 310 Lighting Calcs.xlsx

Improving Insulation for Ludwick and Fire Station

Why insulate?

A majority of buildings built prior to 1974 were built without insulation, and consequently, consumed excessive amounts of electricity through heating and air conditioning. The Ludwick Community Center and SLO City Fire Station #2 are both suspected to have little to no insulation, as both were built in the 1950s.

Improving the insulation of buildings helps maintain indoor temperatures; in the summertime, insulation reduces the amount of outdoor heat that penetrates into the building, while in the wintertime, insulation reduces the amount of heat that escapes from the building. Therefore, improving the insulation of a building can significantly reduce the need to run HVAC systems.

In technical terms, improving the insulation of building walls corresponds to an increase in their R-value. The R-value of a wall is indirectly proportional to rate at which heat can flow through it:

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Determining A

Because insulation is intended to keep a temperature differential between the outside of a building and the inside of a building, it is typical for only the exterior walls of a building to be insulated. The surface area of these walls can therefore be used to determine the rates of heat transfer into and out from a building. Floor plans of both the Ludwick Community Center and Fire Station #2 were acquired for this purpose.

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From these floor plans, the surface area of all external walls for both Ludwick and the Fire Station were determined to be 670 m2 and 290 m2, respectively. It is important to note that these are rough estimations of surface area, and do not account for radiative and convective losses through windows.

Determining ΔT

For purposes of this project, it was assumed that the interior temperature of both Ludwick and the Fire Station were desired to be kept at 22˚C (72˚F) while in use. Using the average high and low temperatures of the SLO area for each season, the outdoor temperature during any given daylight hour was estimated using a quadratic fit.


An hourly temperature difference was then calculated between the ambient temperature modeled in the above graph and the desired indoor temperature of 22˚C.

Determining R

The exterior walls for both Ludwick and Fire Station #2 were assumed to be constructed out of the following layers of material, in order from the exterior of the wall to the interior; 1 cm thick stucco, 0.8 cm thick plywood, 15 cm thick air gap, and 1.6 cm drywall (gypsum board). The R-values of these layers were determined to be 0.014, 0.07, 0.305, and 0.092 m2-˚C/W, respectively; thus, the total R-value of the exterior walls was estimated to be 0.48 m2-˚C/W.

Spray Foam Insulation
Removing either the stucco-plywood layers on the exterior of the walls or the drywall layer on the interior of the walls to fill the 15 cm air gap with batt insulation was assumed to be far too costly a process to be financially feasible. Simpler, more economical installation processes were consequently considered, the most feasible of which was spray foam installation. In this process, a 1 to 2” diameter hole is cut through the gypsum layer of the wall into the 15 cm air gap. A hose is then fed into the hole which sprays expandable polyurethane foam into the air gap.

15 cm of expandable polyurethane foam has an estimated R-value of 3.6 m2-˚C/W. However, due to the presence of internal wall studs, windows, doors, and difficult-to-reach areas, it was assumed that the spray foam installation process would fill only 67% of the air gaps from the base of the walls to the junction where they met the roof. Therefore, the foam was recalculated to have an R-value of 2.4 m2-˚C/W. The R-value of the exterior walls with the air gaps 67% filled with polyurethane foam was calculated as 2.58 m2-˚C/W; thus, the foam insulation was estimated to improve the R-values of the walls by 2.1 m2-˚C/W.
Determining dQ/dt and Annual Energy Saved
Using the hourly temperature differential and surface area of each building, hourly rates of heat transfer were determined for both Ludwick and the Fire Station assuming no insulation (R = 0.48 m2-˚C/W) and spray foam insulation (R = 2.58 m2-˚C/W). These rates were assumed to remain constant for an hour, thus yielding hourly heat losses (or gains) for both no insulation and spray foam insulation scenarios. The differences in these heat losses (or gains) were summed to represent the amount of heat retained (or kept out) in the buildings as a result of installing spray foam insulation.
However, the heat retained via insulation is not representative of the total energy that would be saved via insulation. Heat pumps or air conditioning units would have been used to intake or expel heat in absence of the insulation. Therefore, it is the energy saved by not running heat pumps and air conditioners that is the energy saved via insulation.

Both heat pumps and air conditioning units are able to move more than 1 joule of heat for every joule of electrical energy they use.

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The hourly amount of heat retained via insulation is divided by the maximum efficiency of the heat pump or air conditioner (which also changes hourly as dQ/dt changes hourly) to yield the hourly amount of electrical energy saved via insulation.

The Ludwick Community Center is a venue for city events and is only occupied when an event is being held. Therefore, it is estimated that the Ludwick Community Center is only occupied for approximately 4 hours each day. A Microsoft Excel spreadsheet calculating the amount of electrical energy saved each 4-hour day by Ludwick in the summertime is shown in the following figure.
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Note that the daily Btu saved (highlighted cell) is multiplied by a factor of 4 hours/14-hour day. The total Btu’s of electrical energy saved per season were calculated by multiplying the amount of electrical energy saved per day by 91.25.

Similar spreadsheets were compiled for the spring, winter, and fall seasons. The annual amount of electrical energy saved if the Ludwick Community Center insulated their walls was consequently calculated as 3,700,000 kWh/yr.

Unlike Ludwick, the Fire Station is occupied for 24 hours each and every day. Therefore, it is assumed that during typical waking hours (7:00am to 10:00pm), the station is to be kept at the aforesaid temperature of 22˚C. Spreadsheets like those compiled for Ludwick were also compiled for the Fire Station. The annual amount of electrical energy saved if the Fire Station insulated their walls was consequently calculated as 3,700,000 kWh/yr.
The number of kWhs saved per year by both Ludwick and the Fire Station are excessively high. In reality, the energy saved by installing insulation is likely much lower than these estimates. The current methodology of determining these values of saved energy should be reviewed for use in future studies.

Determining CCE and CAC
The cost of installing spray foam insulation to a building (link) is estimated to be $20.00/m2 of wall. The costs of installing insulation to Ludwick and the Fire Station were thus estimated to be $14,400 and $6,300, respectively. For purposes of calculating the cost of conserved energy (CCE) and the cost of abated carbon (CAC), the following assumptions were made:
– A 15-year loan with a 7% interest rate would be taken out to pay for either of the insulation installations
– Electrical energy saved by installing insulation would have been otherwise produced by single cycle NG, which has an efficiency of ~33%.
– Average cost of electrical energy in California is 15₵/kWh
The CCE for an insulated Ludwick center and an insulated Fire Station was calculated as $0.0001 and $0.00014, respectively. The CAC for an insulated Ludwick center and an insulated Fire Station were both calculated as -$260/ton CO2. These excessively low values are unrealistic and are a result of the excessively high number of kWhs that was predicted to be saved. To reiterate, a deeper study than the one presented here should be conducted before any reasonable CCE and CAC values are asserted.

Improving Roofing Technologies for Ludwick and Fire Station

Solar Panels

The roof on Fire Station 2 seemed optimal for solar panels. The station has a large, open roof space that would be perfect for solar panels. In addition the roof of the fire station will never be obstructed by buildings or trees due to the station doubling as a radio transmitter with atennas on the back on top of the roof. The size of the Ludwick Community Center looked promising but we learned that solar panels installed had already been installed. We were unable to obtain any data from these solar panels but did some estimates based off the size and number of panels.
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In making the calculations we found the area of available roof to be about ~950 sq ft (including setback and space needed for the rooftop antennas) at fire station 2.This allows for the total number of about 54 panels each roughly 18 sqft, that could fit on the open side of the roof. We calculated average energy per year was with a performance ratio( of .77 and solar panel yield at 22% and solar irradiance was approximated to be ~1900 kWh/m²yr (

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The biggest variance we found was in the total price with installation. We were able to get a quote from A-1 Contractor Inc ( JA solar( for forty 320W panels with installation was about $42,000.Our loan was approximated to be taken out with 6% interest and paid back over a 20 year time frame (A-1 Solar).We learned that local governments are unable to qualify for all of the subsidies that residential homes receive ( This could change the price for San Luis Obispo City by as much as 33% with prices ranging from ~$1,000-$1,400 per panel.

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The city would need to attain panels below market value, ~ $700 a panel, in order to be economical. However, solar panels promise to greatly reduce GHG emissions and with technology in pv panels consistently improving hold great potential to become economically advantageous.

Cool Roofs

In comparison to installing solar panels we also looked into reflecting the solar heat both the Ludwick Center and the Fire Station 2 Cool roofs by a factor of 4. Overall a cool roof will lead to less heat in the environment by reducing the need to the use air conditioning systems. (

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The calculations for square footage vary from that of the solar panels because our goal would be to completely cover the roof. The Ludwick has a large portion of flat roof which already seems to have a high reflective surface. We decided to calculate the impact due installing a cool roof on the large gym portion of the building in the middle. We focused on a study by Lawrence Berkeley National Laboratory and the climate zone of San Luis Obispo for our calculations on cool roofing ( .

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The cool roofing was estimated to be $0.10 more per tile than regular roofing and would only be recommended if the roof was already being replaced.It is important to note that while even though San Luis Obispo has a temperate climate, cooling systems are installed and used at the buildings of interest. One drawback we did find, was the potential for cool roofing to lower solar heat in the winter months and thus lead to use of a heater.

Future project outlook

All of the energy retrofits we proposed are feasible, but in order to be implemented, more detailed studies could be conducted. Each of the four retrofitting options can be developed into individual projects and be investigated at much greater depths with more accurate modeling techniques. More developed projects could potentially motivate the city invest in some of these retrofitting options and consequently reduce greenhouse gas emissions.

Unfortunately, making reliable contacts with SLO city was fairly difficult. More intimate contacts should be made and continually fostered in order for this project to ever be implemented.

Current Project Members

Spencer.jpg Spencer Dietz is a 5th year Physics major at Cal Poly, also taking courses in biology, microbiology, and organic chemistry. He believes in using our resources efficiently and effectively to accommodate people without making drastic changes in everyday life.
Zach.jpg Zachary Shockley is a 4th year Physics major at Cal Poly. He has a passion for sustainability and renewable energies. He hopes to either teach Physics at the high school level or work as an environmental consultant/coordinator.
Alfi.jpg Alfredo Medina is a 2nd year Physics student currently doing research with Nathan Keim. Upon completing his degree he is interested in attending graduate school to further his education.
Josh.jpg Joshua Brinkmann is a 4th year Materials Engineering major and Physics minor. Upon graduation, Josh hopes to contribute to the integration of more sustainable materials in the construction industry.
slo city emblem.jpg There were a variety of contacts in the city of San Luis Obispo who provided valuable information used in this project:

Garret Olson – San Luis Obispo City Fire Chief
Bob Bisson– San Luis Obispo City Fire Battalion Chief
Ryley Washbish – City of San Luis Obispo Recreation Specialist
Marcus Carloni– City of San Luis Obispo Special Projects Manager
Bill Humphrey – City of San Luis Obispo Parking Coordinator
Chris Read – San Luis Obispo County Planner
Ian Clements– Neal Lighting and Control Solutions

– Please put the link on the word itself.
-I find this an excellent intro statement.
– You have little else. What exactly do you propose to do?
– Please provide calculations on cost of conserved energy for (for instance) lighting retrofitting. There still needs to be a considerable amount of work on this project. Please come visit me as a group if you need help and/or direction.

-where are these data? Can you provide a direct link to the data? What about the Ludwick center? Didn’t we find that this is very inefficienty?