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ground source heat pumps in texas school district.

by:NULITE     2019-08-22
Independent School District (LISD)
Located in one of the fastest growing suburbs of Austin, Texas.
36 buildings in the area that use soil source heat pumps for maintenance (GSHP)
An average Energy Star rating of 2010 is 97.
1 LISD develops ateam for local design engineers, ground loop contractors, general contractors and architects who interact closely with construction, maintenance and energy management personnel.
Teamwork is essential as the new primary school increases at an annual rate and the construction schedule is very tight. The fast-
The rhythm building of the LISD school did not have a negative impact on energy consumption, as the average Energy Star rating of the new school exceeded 99.
Figure 1 provides power consumption for the whole year
Electric Building.
Cost of turnkey construction of the recently completed GSHP system (
Air conditioning, outdoor air, control and ground loops)
The price is between $20/[ft. sup. 2]to $24/[ft. sup. 2]($215/[m. sup. 2]to$260/[m. sup. 2])of floor area. (2)
Considering the large number and cost of outdoor air systems with energy recovery, the cost of these systems is not
The GSHP system saves energy and maintenance costs.
With more than 21,000 vertical holes and 2,100 miles of U-
Heat exchanger pipe ,(3)
The surrounding area of Austin may be the most concentrated area of GSHP institutions and commercial buildings in the United States. S.
In 1994, LISD adopted a lot of local practices, but also did something different to reduce the cost of installation and maintenance.
The Gshp system is a simple, single approach where each classroom heat pump is connected to a separate ground return
Turn off the circulating pump.
LISD brought together its major engineering companies, general contractors, several architects and their employees to assess 1997-98.
School boards and supervisors support additional upfront spending in terms of quality, but they want to get a proven life --
Cycle cost based on measurement data rather than simulation performance.
The team chose to apply something in the LEED rating system, but finally decided to use energy star as an evaluation tool because it was based on the data actually measured. (4)
The specific results of the assessment included long-term underground heat exchangers, improved specifications for backfill materials and greater vertical drilling spacing compared to the practice in 1980.
Details will be discussed later.
LISD repeated the System Assessment in 2002-
Operating system and again at 2012.
A major result of 2002
03 The process is to implement a startup program
Start and debug.
The main technical improvement is to abandon the customized classroom console unit and place vertical updraft heat pumps and ventilation equipment in the attic in the corridor.
It is difficult to maintain the console unit located in the classroom, and the units installed in the vertical mezzanine are inherently easier to access for maintenance personnel.
2012 the main findings of the assessment are the following amounts
The time used only in some facilities is usually very small.
This discovery provides additional support for the initial design selection, and these units do not need to turn on the central equipment to adjust a limited number of areas and take up the load.
Although there are about 5,500 heat pumps in the area, the impact of LISD on equipment manufacturers is limited.
For example, a major equipment manufacturer is using insulation that has been separated after several years of operation and is sometimes sucked in by an indoor fan.
They chose to continue using fiberglass during the manufacturing process, but in fact to meet the needs of the area, they took the cable apart and installed different insulating materials.
This leads to a bigger problem that LISD no longer uses this manufacturer.
The last key issue that LISD learned through years of experience is the importance of the owner being able to choose a design engineer rather than an architect.
The design engineer\'s point of view LISD used almost exclusively a mechanical and electrical engineering company whose principal responsible person participated in GSHPs for the first time in 1988.
The experience began in six classrooms in a primary school in Austin.
At that time, there was very little information on the design of commercial and institutional buildings in terms of vertical heat exchanger specifications, installation methods, hole spacing and length.
The suggestion of the heat pump manufacturer is 240 drilling perton (48 W/m), 10 ft (3 m)
The borehole separates and rings filled with pea gravel.
The contractor drilled the hole and inserted the tube into the \"dry\" hole, but the time was running out and the filling was not inserted that day.
The next morning, the crew returned to the scene and found a large amount of spaghetti --
It looks like a black tube. The hole is gone.
The pipes were abandoned, and the process was repeated with random efforts, eventually sealed with concrete.
After the grounding circuit is installed, the connection device runs smoothly.
After the unit was started, the engineer never heard from the owner.
Since this rarely happens in traditional systems, he realizes that it may be worth it.
The practice of continuous improvement and the single point of responsibility for the whole system has been successful.
The MEPfirms designed the whole system, including the ground loop and the control loop, and avoided the temptation of the contractor or supplier default loop and the control design.
The ground loop is longer at 300/ton (39W/m)
At least 20 feet apart (6 m)
The filling material is more heat-conducting.
However, the concept of the overall GSHPs still exists.
Another design challenge is that the supply area of the Edwards Aquifer is located below the area and extends to the southwest of San Antonio. (5)
The main source of water for the city and surrounding cities is the reservoir.
Therefore, water treatment chemicals such as those that inhibit corrosion are not used in Leander.
By using high-
Density Polyethylene (HDPE)
For internal and external pipe loops.
Pumps often have copper sheets with stainless steel or plastic impeller.
In order to deal with the expansion properties of high density polyethylene and fire protection specifications, the internal pipe network was modified. Larger water-to-
Compared with smaller units that provide services to classrooms and offices, the cooling efficiency of air heat pumps at 1990 s is significantly reduced.
In larger public areas, they are quickly replaced by traditional air.
Cooling equipment.
Another adjustment for new schools and renovations is the use of a dedicated outdoor air system (DOAS)
The ventilated air after pretreatment is decoupled from the heat pump.
To improve the energy star\'s average score of 97 points, The LISD team is considering using GSHPs more widely in public areas and using the rich waste heat to pre-hot water in the kitchen and dressing room shower.
The current practice of using a dedicated outdoor air system to separate the ventilated air from the heat pump supply pipeline may be adjusted. Water-to-
Water heat pump can replace air-
Cooling cooler as a supplementary pre-treatment option.
These alternatives need to be analyzed to determine whether they provide good economic value for the region.
The view of the general contractor over the past 15 years, the general contractor of many GSHP projects in LISD has confirmed the value of continuous improvement.
Although the apublic entity has to follow some rules that make it challenging to choose the team it considers best, it has managed to surround itself with team members, quality contractors, subcontractors and engineers
Moving to \"best value mechanical equipment procurement\" before and outside the tender submitted by the mechanical subcontractor will benefit the construction process.
Equipment specifications need not
Proprietary rather than specifying a specific manufacturer.
Because there are all kinds of nuances in each manufacturer (
Some of them are proprietary)
Owners and engineers have the opportunity to assess the extent to which the alternative meets the needs of the region, rather than accepting low-cost BIDs provided to mechanical subcontractors.
Bringing engineers and regional staff closer to the procurement process of mechanical equipment can benefit for a long time
System performance and lower first cost.
For owners like LISD, it is important to plan the ground loop for future expansion.
A thorough on-site investigation is recommended as whenGSHPs is the preferred system even before purchasing the property.
This can avoid the characteristic of increasing the cost of the gshp system due to the geology under the surface.
From a maintenance point of view, since the use of a single heat pump eliminates the possibility of catastrophic loss of the central system, the maintenance supervisor has become fond of GSHPs.
Only one classroom is lost when a fault occurs.
The staff suggested that a shift to a central system would result in more redundancy, resulting in increased installation costs.
A common concern expressed by service personnel who are not familiar with GSHPs is that there are so many compressors that may need to be replaced frequently.
Experience with LISD shows that there is no problem with compressor replacement, although it has some problems with capacitor and expansion valve failures.
It also found no condenser coils with problems.
Maintenance staff like the heat pump located in mezzanines and appreciate the movement of the console units installed from the ceiling and the classroom.
The second option is to open the closet in the hallway.
LISD has 24 primary schools, about 100 heat pumps per unit, 8 secondary schools, 200 heat pumps per unit, 5 high schools, and about 500 heat pumps per unit.
Since each heat pump has its own grounding circuit, the leakage problem often attracts people\'s attention.
There are 10 to 12 loops with makeup water that are located in the old school of American University
The pipe is removed from the standard elbow by the loop contractor.
New school of prefabricated U-
There seems to be no problem with the tube used.
In the first or second year, there are some situations when the cycle pressure drops, but each service technology has a portable bladder tank with a probe that will pass through the pressure/temperature on the heat pump
Most problems with pump tripping
The output is caused by air in the line, solved by moving the pump down from the highest point in the circuit (
Photo 1, page 36).
There are many buildings in LISD (46)
Few HVAC service technicians (eight).
While the main service work is outsourced, the simple GSHPsystems used in the region allow a large number of buildings to be replaced by a small number of staff.
The energy manager\'s point of view LISD the energy manager did not notice an increase in energy use or ground loop temperatures due to the severe drought and heat waves experienced in the region over the past three years.
Newer buildings, such as rouse and Vandergrift high schools, have not yet become energy stars, but energy use is much lower than those old high schools that have ratingin in the medium term. 90s.
Challenges handled by staff
The staff who liked the room were very comfortable.
\"Most rooms have air conditioning for more than 30 minutes, just press the button (
Up to three pushes).
Two other rooms. to-
4 hours reverse timer coverage. Smart-
Data statistics have also been tried, but creative teachers use information on the Internet to be smarter than these devices.
GSHPs can accept these types of violations and provide excellent energy performance.
The circular contractor\'s point of view proposes, installs and, in some cases, installs a variety of new and innovative underground heat exchanger designs to reduce costs. (6)
An observation of the austin area ground loop contractor reveals why simple and durable high density polyethylene U-
Tubes of greater length and depth can be installed at a lower cost than finer alternatives.
Repeated trials over the years have solved the challenge of optimizing the cost and performance of underground heat exchangers.
In a recent project with good drilling conditions, the contractor hopes to finish it by the end of the week.
They installed thirty.
Vertical U-300
There are underground heat exchangers for three rigs in one day.
Being able to drill many holes so quickly can be attributed to the well-
In this case, the equipment is maintained and experienced, especially the powered drilling rig.
Because local companies have been doing GSHPs for more than 20 years, they have to learn (
Often from each other)
How to Survive effectively.
A major challenge for these contractors is the \"Feast or famine\" nature of the business.
The investment in personnel and equipment to maintain the ability to install a large number of underground heat exchangers in a short period of time may be overwhelming.
Therefore, in the slack time of one month, two months or more, the cost of carrying personnel and other expenses must be embedded in the price of the grounding circuit installed during the peak period.
During a live visit, when I saw the Cycle Contractor using two drill machines leased from a competitor, I observed a way to solve the problem.
Draw a page from LISD\'s \"team work\" mantra, with some loop contractors either renting strict equipment during peak hours or subcontracting the installation to competitors.
These contractors also provide a lot of feedback to the engineers and are willing to consider the change is very important to win the respect of the drilling contractor.
However, experienced engineers also learned that,
The capability ground loop contractor is the same, and in order to ensure the quality of the system, some contractors have to receive closer attention than others.
Other lessons learned by Leander include: * The owner must be willing to invest in long-term economic value.
* The plan must be evaluated regularly by the owner.
* The results should be based primarily on measured energy indicators like Energy Star.
* The owner must hire highly qualified technical and maintenance personnel.
* Cooperation and respect between owners, contractors and designers is essential.
* High quality and flexible design engineers are critical.
* Maintenance personnel can provide valuable information about the quality of the system and should be an integral part of the design team.
* Despite years of experience, high quality ground circuit contractors have made impressive enhancements to the installation efficiency of vertical circuits.
* In a very warm environment in Central Texas, the school\'s simple unified cycle GSHPs shows impressive results. References (1. )ESL. 2012.
Energy Star marked K-
Twelve schools in Texas are owned by leander ISD. (2. )MEP. 2012.
MEP engineering company Leander isd us builder expenditure record(3. )Ball, 2013.
Geothermal facilities closed loop in Austin area.
\"Personal communication with Lonnie Ball.
Drilling CompanyAustin, Texas. (4. )EPA. 2010.
\"How the rating system works.
Portfolio manager overview of energy. U. S.
Environmental Protection Bureau. (5. )HARC. 2012.
Advanced Research Center Houston
Edwards Reservoir
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