There are other issues that should be considered in the decision process. The owner will have a strong interest in the first cost and construction schedule just discussed; a list
Table 5-2. Construction Schedule Impact
Alternative 1 Central Fan Systems Central Chilled Water
Alternative 2 Floor-by-floor Fan Systems
Central Chilled Water
Alternative 3 Floor-by-Floor DX Systems
Central Cooling Tower ISSUE — GENERAL COMPLEXITY OF INSTALLATION
• Central mechanical equip- ment room space and com- plex construction technology for both chiller plant and fan system locations.
• Chiller plant space is required with the need for more com- plex construction technology.
• Areas that contain complex construction technology are limited.
• Requires piping of a major chiller plant.
• Requires piping of a major chiller plant.
• No major chiller plant. • Cooling tower only. • Chiller plant location critical
to construction schedule.
• Chiller plant location critical to construction schedule.
• Chiller plant is not required.
• Heavier slab construction at central mechanical equip- ment room.
• Heavier slab construction for chiller plant only.
• Very limited special slab construction.
• Extensive complex duct- work in central mechanical equipment room.
• Limited ductwork, repetitive fan room arrangement on each floor.
• Limited ductwork, repeti- tive fan room arrangement on each floor.
Chapter 5—Central Mechanical Equipment Room vs. Floor-by-Floor Fan Rooms | 51
of other matters of concern to the owner is provided in Table 5-3. The discussions under “Marketing/Electric Metering” are of special consideration in developer buildings. An issue in lease negotiations for developer buildings is the allocation of operating costs. In today’s market, most, if not all, multitenanted buildings have separate electric meters for each tenant. These separate meters will cover all of the tenants’ lighting and small power consumption, but the energy used to provide heating, ventilating, and air condi- tioning is a much more difficult issue.
For a multitenanted building and lease terms of multiple years during which the cost of energy will fluctuate as will the operating labor for the building, the problem can be quite complex.
The difficulty is most apparent in developer buildings using Alternative 1 with cen- tral fan rooms and central chilled water. For those projects, the operating energy costs are paid for by the owner and a means to pass this cost on to the several tenants is required. For example, if all tenants utilized their space from 8 a.m. to 6 p.m. on week- days only, the problem would be relatively simple, but many professional service firms in the fields of accounting, law, architecture, and engineering typically operate on
Table 5-3. Owner Issues
Alternative 1 Central Fan Systems Central Chilled Water
Alternative 2 Floor-by-Floor Fan Systems
Central Chilled Water
Alternative 3 Floor-by-Floor DX Systems
Central Cooling Tower ISSUE — MARKETING/ELECTRIC METERING
• Tenant lights and small power can be metered directly.
• Tenant lights, small power, and fan energy can be metered directly for any floor with a single tenant. Multi-tenanted floor will require allocation of fan energy only.
• Tenant lights, small power, fan and cooling energy can all be metered for any floor with a single tenant. Multi- tenanted floors will require allocation of fan energy and cooling energy only. • Fan energy and chiller plant
energy, as well as heating energy, operating costs are allocated unless heating is by electric resistance heat.
• Chiller plant energy, as well as heating energy, operating costs are allocated unless heating is by electric resis- tance heat.
• Heating energy operating cost must be allocated unless heating is by elec- tric resistance heat.
• Other common building operating costs are allo- cated.
• Other common building operating costs are allo- cated.
• Other common building operating costs are allo- cated.
ISSUE — OPERATING COSTS • For normal operating day,
operating costs for all floors occupied will be lower than for Alternative 3, approximately equal to Alternative 2.
• For the summer operating day, operating costs for all floors occupied will be lower due to lower energy consumption than for Alter- ative 3, approximately equal to Alternative 1.
• For the summer operating day, operating costs for all floors occupied will be higher due to higher energy consumption than Alterna- tive 1 or Alternative 2 due to less efficient DX com- pressors.
• Overtime operation requires the chiller plant to operate in the summer. With variable-speed fan control and headered sup- ply and return fans, energy costs equal to Alternative 2. Operation more cumber- some. Fan and chiller plant costs must be allocated.
• Overtime operation requires the chiller plant to operate in the summer but otherwise simple. Chiller plant cost must be allo- cated.
• Overtime operation sim- plest but probably higher in cost than Alternative 1 or Alternative 2. Single-floor tenant cost for cooling tower only must be allo- cated.
extended schedules of overtime, which can extend into the evenings as well as week- ends. To solve this problem, a relatively complex and—for the tenant—possibly expen- sive arrangement must be provided to allow the tenant to obtain air conditioning in periods other than the normal occupancy hours of most offices. The arrangement should include the cost of the labor and energy to operate the chilled water plant and any fans that may be required to deliver air conditioning to the tenant. Most leases include the heating cost as a landlord’s cost and, since heating costs are nominal, there is a lesser problem with that component of operating cost.
One of the primary advantages of Alternative 3 is that the cost of energy for air con- ditioning for any single-floor tenant can be directly metered to the tenant on an electric meter. If electric heat rather than fossil fuel heat is utilized, that cost can also be placed on the tenant’s meter. To express it more directly, the problem is simple and the solution straightforward with Alternative 3. Overtime operation for firms that operate on extended hours is equally simple with only the cost to operate the cooling tower and any necessary labor being subject to an allocation basis. Alternative 2 again is more com- plex in that the costs of operating the chilled water plant in warm weather must be allo- cated with only the fan energy, lighting, and small power in the local floor-by-floor fan room being on the tenant’s meter.
The issue is a difficult matter, but the use of Alternative 3 with floor-by-floor DX units has achieved much of its application because it provides a solution that appeals to the landlord since the landlord can negotiate a lease with minimal concern for any need to allocate costs and appeals to the single-floor prospective tenant because the system can be operated when needed and with the knowledge that the costs to operate the sys- tem are predictable and under the tenant’s control.
Moreover, since condenser water is required to operate any one unit in a project on overtime, the provision of condenser water to tenants with supplemental cooling needs for information technology rooms or a limited data center can be easily accommodated through the operation of the cooling tower and condenser water pumps to satisfy both needs.
The marketing advantage in the multitenanted developer building with Alternative 3 is clear. In owner-occupied and corporate headquarters buildings, the issue of the allocation of operating costs is not a real issue and, as a result, these buildings will more typically use either of the chilled water solutions that are part of Alternative 1 and Alter- native 2.