The existing First Presbyterian Church facility in Oak Ridge, Tennessee consists of three buildings. 1) The Sanctuary and Fellowship Hall building is a one story building that has approximately 10,300 sq. ft. of space and is conditioned by five 20 year old Heat Pump units of abut 43 tons capacity. The Sanctuary is used on Sundays from 8 am until 1 pm, and again from 5 to 8 pm. The Fellowship Hall is used most evenings for meetings. 2) The Activities building is a two story U-shaped building that has approximately 9,900 sq. ft. of space and is conditioned by seven 35 year old DX/Gas units of about 31 tons capacity. Approximately ½ of the building is used for office space about 40 hours/week with the rest of the building used for daytime and evening meetings. Numerous hot and cold spots currently exist in the building. 3) The Education building is a two story rectangular building that has approximately 5,500 sq. ft. of space and is conditioned by two 5 year old DX/Gas units of about 20 tons capacity. Approximately ½ of the building is used for daycare about 60 hours/week. On Sundays the whole building is used between 8 am until 1 pm.
Replacement of the Sanctuary and Activities building HVAC units is presently needed, while the Education building units do not need to be replaced at this time.
The buildings are structures having a wall assemblies that provide a minimum insulation level of R-11 and a roof assembly of R-20.
The lighting systems are primarily fluorescent for most of the areas. The internal loads were considered to be typical for religious, office, or educational facilities as appropriate. Ventilation air is not currently provided for the facility and therefore does not comply with the guidelines of the current ASHRAE Standard 62.
Two types of HVAC Systems were modeled in this study – a replacement of the existing HVAC System with updated equipment that provides outside air ventilation and a Geothermal-based HVAC System Option.
AIR SOURCE HEAT PUMP SYSTEM (WITH GAS, AUXILIARY HEAT (DUAL FUEL)
This type of HVAC System is capable of providing either heating or cooling to the area(s) being served based upon the setting of the thermostat that controls the system components. By being properly sized, the respective HVAC System components can usually maintain thermostat set-point conditions under normal conditions. When an area thermostat/sensor is satisfied, the system shuts the compressor/gas burner off. Normally the fan remains on when the space is occupied, and the air required for ventilation purposes is still supplied.
One drawback of this type of HVAC System is the range of operational efficiencies of the various System components during peak heating and cooling conditions. The heating is provided primarily by the heat pump component until the outdoor temperature drops below 32 Deg.F. At this point the gas heat provides the system’s heat. Likewise, the air-cooled component cooling capacities are typically de-rated between 10% to 15% off their nominal cooling capacity when outdoor air temperatures exceed 85 Deg.F.
This present deisng of the activities building heating ventilating does not provide satisfactory zone control for many areas.
This study includes installation of the Acutherm register & bypass in each zone. The application of the Acutherm System will allow individual control for each register zone. This is to address the problem identified in the activities building, of not having adequate zone control. See attached literature.
GEOTHERMAL HEAT PUMP SYSTEM (GEO)
The proposed Geothermal Heat Pump System (GEO) is comprised of extended-range hydronic heat pumps that are connected to clusters of boreholes. This HVAC System Option does not require a boiler, cooling tower, chiller or any other auxiliary heating/cooling components external to the hydronic loops.
This installation would require approximately 60 boreholes having a minimum depth of 300 feet. Each borehole would have a U-tube loop of at least 600 feet of 1” ID high-density polyethylene (HDPE) tubing. This tubing is seamless and continuous with thermally fused joints. Typical borehole installations are guaranteed for 25+ years and can therefore be located just about anywhere (e.g. under asphalt pavement, parking areas, etc…). The actual number of boreholes can be determined after a “test bore” and corresponding thermal conductivity evaluation is conducted for the site.
The loop heat transfer medium (typically water) is distributed to/from the U-tube piping in the boreholes by supply and return distribution headers. The heat transfer medium enters a bore-hole’s U-tube loop, goes to the bottom, and returns to the top and is directed to a return distribution header. Each borehole is back-filled with either bentonite or clean bore fines in order to achieve better heat transfer with the earth’s strata.
The Geothermal Heat Pump System is capable of providing either heating or cooling throughout the year. With the extended-range, high efficiency hydronic units the Geothermal Heat Pump System Option is capable of providing the best humidity control of the HVAC System Options considered. The combined operational efficiencies of the components in this HVAC Option allows the total heating and cooling capacities to be approximately 15 % lower than the ASHP Option. As with the other HVAC System Options, a humidistat must be added to the control configuration of the thermostat/sensor for the respective Geothermal components.
It is intended for the purposes of this study (pricing, etc.) that the number of boreholes immediately installed be sufficient to serve all three buildings. Because of various occupancy times of the buildings the borefield does not have to be sized based on the total tonnage required in the buildings, but can be smaller by taking advantage of diversity. The first stage of construction would be to install the borefield and the new HVAC units for the Sanctuary and Activity buildings. A connection would be left for the Education building to have geothermal units added at a later date. The cost of the borefield is totally allocated to the Sanctuary and Activity buildings.
The control of the HVAC System components that are being evaluated in this study is considered to be done primarily with thermostats located in the respective spaces of the areas being served by the HVAC System components. The new controls integrated into the study costs also include
the humidistat and ‘humidity’ control components that control the overall operation of the proposed energy-recovery systems with the components of the respective HVAC System option.
The GEO Option provides the “best” humidity control option due to the ‘extended range’ coil configuration.
We are providing a separate quotation for a refined “Energy Management System” such as is used on schools & other large installations.
3. UTILITY RATES For all of the HVAC Systems considered, the charge for electric power and energy was based upon the City of Oak Ridge rate schedule. The breakdown of demand and energy consumption charges utilized in the two studies is given below:
Customer Charge = $30 per month
1st 15,000 KWH = $0.07/KWH
KWH > 15,000 = $0.036/KWH
1st 50 KW demand = $0.00
KW demand > 50 = $9.94/KWD
The gas costs for the representative gas rates that were integrated into the respective analyses for the HVAC Systems utilizing gas-fired equipment are given below:
Summer rate = $0.85/therm
Winter rate = $1.30/therm
The load calculations, system evaluations and economic considerations were conducted with computerized simulation software from both the Trane Company and the National Institute of Science and Technology (NIST). The building conditions and operation were modeled according to the following parameters:
Buildings will be occupied as previously described,
During unoccupied periods, heating setting was 55 Deg.F. and cooling setback was allowed to float,
Domestic water heating costs were considered,
Ventilation/outside air heating and air conditioning costs were determined for each HVAC System Option considered; the primary conditioning of the outside air is by means of energy recovery components with any conditioning augmentation being done with components (and utilities) similar to the respective HVAC System Option that the energy recovery system interfaces with,
The installation costs for the respective HVAC Systems considered were determined from averages of local installations, national cost averages from Means Construction Cost Data Books and reports provided by TVA,
Maintenance cost factors for the respective HVAC Systems were determined from information provided by TVA and ASHRAE. The basis for the information was an ASHRAE Technical Committee Research Project 382-RP with minimum cost levels being applied,
Escalation factors of 3% annually were used for utility and maintenance costs in the Trane program; the NIST Building Life Cycle Cost (BLCC) program incorporated a Discount Rate of 3.1%, general inflation rate of 3% and Department of Energy Projected Fuel Escalation Rates for electricity and natural gas,
Amortization was based upon an interest rate of 8.5% for 90% of the installation costs being financed for 10 years,
No taxes were included in the fuel and utility cost rates.
We fell that under the current Energy Climate that Natural Gas prices will exculpate much faster than indicated in the study.
5. CLARIFICATION This study was performed on commercially available manufacturer’s software using input data known from currently operating existing systems, and modeled to match current known costs. The weather data, operating data, and manufacturer’s data and other algorithms are based upon “averaged” values in data banks and known costs.
Due to the magnitude of assumptions and averaged values integrated into the various calculation formats, this study is intended to be only a comparative, practical guide for the various HVAC Systems being considered for the Oak Ridge Presbyterian Church facility. It should not be assumed that it could be used as anything else. No guarantee of the respective system’s values is implied or warranted. Any other project must be substantiated upon its own merit.
Many items of incidental nature were purposely omitted (i.e. total facility water usage, insurance, taxes, etc…) from this study.
6. CONCLUSIONS The results of this study are summarized in the tables shown in Part II – Operation and Maintenance Costs.
The two different Life Cycle Cost Analysis Programs that were incorporated in the economic evaluations produced similar results for the HVAC Systems considered for the various areas in the Oak Ridge Presbyterian Church facility. Both the NIST BLCC and Trane Programs’ results indicate that the Geothermal-based Heat Pump System (GEO) produced not only the lowest annual utility and maintenance costs but also the lowest Life Cycle Costs for all HVAC System options considered.
An additional comparison of the HVAC System options for the respective buildings utilizing a Simple Payback format produces the following results. The Simple Payback Period is determined by comparing the difference in installation costs to the difference in the first year’s operating costs (the sum of the annual utility and maintenance costs) after the contractor’s warranty period for the new equipment. For the various HVAC Systems under consideration, the following Simple Payback Period was developed:
Geothermal Comparison to ASHP HVAC System for the combined Sanctuary and Activity Buildings (includes all borefield costs)
Simple Payback Period = $(348,985 -197,838) = $151,147 = 7.7 years
$( 30,697 - 11,184)/yr $ 19,513/yr
PART II – OPERATION AND MAINTENANCE COSTS
Two different Life Cycle Analysis Programs were utilized to develop the results shown in the Tables. The primary differences between the two analysis programs are the way the escalation rates for utility and operating, maintenance and repair (OM&R) costs are determined for future years and the consideration of equipment replacement costs during the life of the study. The Trane Program uses a constant escalation rate (an input value that was listed in Section 4 of this study), and does not have a provision for including replacement costs during the life of the study. The NIST Program incorporates projected escalation rates for utility costs and OM&R costs that have been developed by the Department of Energy (DOE) and can integrate equipment replacement costs for the options being considered during the life of the study.
The primary difference between how the results are shown from the two Life Cycle Analysis Programs is that the Trane Program’s utility and maintenance costs are for the 1st year after the contractor’s warranty period and the 20th year of the analyses. The generated Life Cycle Cost by the Trane Program incorporates all costs over the 20-year study period. The NIST Program’s utility and maintenance costs are totals for the 20-year study period and the indicated Life Cycle Cost is likewise for the entire 20-year study period.
Table 1A. Sanctuary Building HVAC Systems Evaluation with NIST BLCC Program
Table 1B. Activity Building HVAC Systems Evaluation with NIST BLCC Program
TOTAL Investment Costs
TOTAL OM&R Costs
TOTAL Energy Costs
Life Cycle Costs
Therefore the 20 year savings of the GEO System is estimated at $223,254.
Notes apply to the two tables
Notes: Investment costs include capital replacement and residual values. Residual values for initial capital investment and capital replacements are calculated when life extends beyond end of study period. Equipment life for the heat pump components was considered to be 15—17 years for outdoor, air-cooled equipment and 17—20 years for indoor components. Equipment life for the interior Geothermal system components was considered to be 18—22 years.