PE-Services has written an article for a recent issue of Retail Construction magazine (www.retailconstructionmag.com). Over the next month, there will be three posts covering flexibility in Retail MEP Design. Please post a comment or e-mail us if you have any additional questions.

So you want Flexible Lease Space?

One of the primary goals for the MEP design of each retail center, whether a large Life Style Center or a smaller rural strip center, is to have flexible lease space. The question always arises, “What if a restaurant wants this space?” or “What if a tenant takes three spaces?” While there is not a one size fits all solution for every center, there is a series of decisions each developer needs to make prior to beginning the mechanical systems design phase of a new center. Following is a description of various options for Mechanical, Electrical, and Plumbing/Fire Protection along with the pros and cons of each to assist with the planning phase of future retail centers.

HVAC – Since most locations use a model energy code which dictates the amount of lighting that can be utilized in a retail space and ASHRAE 62.1 is widely accepted as the standard for calculating the amount of outside air required for a space, sizing and installing units for a typical retail space under the shell package is not a huge risk. The advantages of doing this include having all the equipment from the same manufacturer and a shorter tenant fit up time. The drawbacks to this approach include the upfront cost of the units before tenants are in place as well as the potential that some other type of occupancy, a restaurant for example, really wants a particular space - thus the need to view design with a balance of cost and flexibility. Below is a brief explanation of the various types of systems which can be utilized in retail design along with the flexibility pros and cons of each.

Roof Top Units (RTU’s) - By far, most owners will opt for the use of package roof top units. These units combine heating and air conditioning into one unit, either electric heat and cooling or gas heat and electric cooling, and typically require a flat roof for mounting. These units can be designed based on the intended use of each space, or if not known at the time, loads can be calculated based on typical retail usage. When utilizing RTU’s there are three options for the shell package: install the units based on typical retail requirements, install curbs only based on intended usage, or install no units under the shell package.

If the developer decides to install the units under the base shell package, placement of the unit can increase flexibility. As long as there are no visibility issues, the units should be set to the front half of the building. This will allow flexibility if the space is leased to a restaurant as the additional units could be placed on the rear of the space where a kitchen would typically be located. This type of application is not only very flexible but increases the speed of future tenant build-outs.

The second option is to place the roof curbs in anticipation of future RTU placement. Since most manufacturers’ equipment utilizes the same roof curb for groups of unit sizes, this leaves the sizing of the equipment fairly flexible. One major cost implication is being locked into a single manufacturer (to match the curb), which will likely increase the cost based on a sole source manufacturer. The advantages of this approach is that the units are not purchased until tenants are identified while allowing the roof work to be done under the base building to ensure a good continuous roofing system by one contractor.

The final option is to put no curbs or units in under the shell. While the advantages are no cost upfront and maximum flexibility for unit placement as tenants are identified, the major disadvantage of this approach is cutting holes in a new roof each time a new tenant moves in.

Split Systems – If there is no provision made for roof mounted equipment, the design will likely require the use of air cooled split systems. These systems require a furnace inside and an air cooled condensing unit located outside the building. While this system is less costly than a RTU it has even more limitation, such as a maximum of 25% (or less) outside air and the typical requirement for inside floor space. Based on these limitations this type of system is typically only utilized in very small spaces.

Central Systems - Strictly from an efficiency and flexibility standpoint, the most flexible HVAC system for large retail and mixed-use applications is a central system consisting of either a chiller/boiler with associated water piping or large RTU’s with main duct runs. These units provide a lot of flexibility; however, the initial cost of this type of system and the requirement for the landlord to prorate energy bills will keep the vast majority of malls, strip centers and stand alone buildings from using this type of system.

Temporary Heat – Most locations, other than those in southern states, require some temporary heat. If units were actually installed on the roof under the shell package, one or more of these units could be utilized as temporary heat. Another option is to provide unit heaters, either gas or electric, and connect them to a “house service” – these units can be relocated as required as tenants occupy spaces.

While there are various options for heating and cooling retail facilities, a close review of each project will help filter the choices. The primary points of analysis should include the size of the development, utilities available, how long the developer plans to hold the property, and last but not least, the anticipated tenant mix.