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Agenda - 06-12-2007-4aa
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Agenda - 06-12-2007-4aa
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8/29/2008 7:07:48 PM
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8/28/2008 11:55:13 AM
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BOCC
Date
6/12/2007
Document Type
Agenda
Agenda Item
4aa
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Minutes - 20070612
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\Board of County Commissioners\Minutes - Approved\2000's\2007
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s <br />Renovatuig the jail will require bringing the site up to code in many areas. One which plays a <br />significant part in HVAC is the outdoor air requirement. Replacing the current air conditioning <br />systems «~ill require an increased amount of outdoor air to be brought into the building to meet <br />the North Carolina State Mechanical Code (Chapter ~1) alld Asluae Standard 62. This is done to <br />increase the indoor air quality within the jail by providing fresh air front the outside and <br />exhausting stale air containing odors, contaminants, etc. from the biiildi.ng. <br />We also explored the option of applying a district heating system to this building and adjacent <br />buildings in the area. We do not recommend districting as an option for this site. Our <br />recommendation is based upon this site having a relatively low load density and a lo~~v annual <br />load. factor. A low load density means that the heating and cooling loads are spread out over a <br />lai:ge geographical area with large areas having no load at all (streets, parking lots, grass areas, <br />etc.). A low annual load factor means that due to these buildings being mostly office areas the <br />loads fluctuate significantly on a daily and yearly basis. The 2000 Asluae Handbook -HVAC <br />Systems and Equipment (Chapter 11) recommends that both oi'these factors be high in order for <br />the economics of a district heating and cooling to make sense. This is typically seen in l) <br />industrial complexes and 2) high rise buildings where you have a high heating aid cooling load <br />per ,square foot of site footprint and more consistent daily and yearly load factors. <br />Also, the cost of the distribution piping for this system would be vet:y large and installation <br />would sigtlificautly disrupt the roads, sidewalks, and grass areas around the buildings in ibis <br />historic area. The coordination with existing utilities and the "tullcnowns" below these areas <br />alone could present a significant challenge and in itself could prove prohibitive. <br />Although not analyzed in this life cycle cost analysis, we considered the options for dealing with <br />HVAC related issues at the I~istoric Caw•thouse and the Court Street Aivzex. Since a district <br />system is nat practical, we recommend replacing the equipment at the Historic Courthouse with <br />like equipment or substituting DX systems in lieu of WSHP. As for the Court Street Aruzex, we <br />recommend. abandoning the underslab ductwork entirely as it can become problematic with <br />respect to humidity atzd indoor air. quality. The limited above ceiling space prohibits installing <br />ductwork above ceiling so we would reconunend small, ductless DX systems such as <br />Mitsubishi's City Multi system to treat the lower level. These systems operate well at low load <br />conditions, providing ,some degree of dehumidification at even the lowest load paints. <br />Considerul~ that the equipment serving t11e second: level is relatively new (1.999 or later) we <br />don't see any need to modify or replace this equipment at this time. <br />BASIC SYSTEM .DESIGN CRITERIA <br />The eventual system design, after conducting the life- cycle cost analysis on the tluee systems <br />listed above and selecting an alternative, vaould include the following (but not limited to): <br />Evaluation of the existing central chiller and air handling units, to detei7nine how they <br />should be replaced within the project budget. <br />Installation of a new energy management system. <br />
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