Agenda - 06-12-2007-4aa - Laserfiche WebLink

Browse Search

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