Cira Centre South
HVAC SYSTEMS
The FMC tower combines HVAC systems for heating and cooling for the different types of spaces. A heat pump system is used on the upper levels for the residential portion of the building, and a VAV system is used for the office portion of the building.
There are four cooling towers on the roof, and these supply both the VAV system on the office levels (below, left), and the residential heat pump system (below, right). A cooling tower functions by rejecting waste heat into the atmosphere through cooling a water stream to a lower temperature. Cooling towers can use evaporation to remove process heat and cool the working fluid.
Residential Levels
For the residential system, the cooling towers are looped with three boilers, also located on the roof, to assist the individual floor heat pumps on each floor during the cold months. A boiler is simply used to heat the water or fluid used in the system. During the hot months, the boilers are not used. The individual heat pumps on each floor are used to set the temperature per room as desired by the resident. A heat pump can be used to heat or cool an area, and is a device that provides heat energy from a source of heat. In this case, during the winter months, the boiler would be used to heat the fluid of the hydronic system, and the heat pump located in the residential levels would fine-tune the temperature. It is probable that there is also a chiller located somewhere in this loop for use during the cold months to initially cool the fluid before reaching the heat pumps (again, used for fine tuning the temperature). There are also separate electrical heating units located in the bathrooms on the residential floors to be used for extra heating in those locations. A diagram of this system can be seen here.
Office Levels
The four cooling towers, located on the roof, also supply the VAV system on the office levels. The cooling towers are looped with three chillers on level 27, the mechanical load transfer floor. The chillers for the VAV system (located on Level 27) are supplied from the cooling towers, located on the roof. A chiller removes heat from a liquid by a compression or absorption refrigeration cycle. These chillers are then looped with the individual air handling units, which are located on each office floor. The air handling units supply air to the VAV boxes. A VAV box supplies a variable air volume to a space, depending on the temperature desired. In the FMC tower, the VAV boxes are integrated with electric reheat boxes, which fine-tune the temperature of the air pumped into the office levels. The exhausted air from the office levels is pumped through an energy recovery unit (there are two located on level 27), and the fresh supply air is conditioned in the energy recovery unit before supplying the air handling unit with the new air. This works by the exhaust air heating or cooling part of the system, which is then rotated so the fresh air can enter through that heated or cooled part, giving it a head-start before entering the air handling unit. A diagram of this system can be seen here.
There are three air handling units in the basement levels that supply air for the office lobby, the residential lobby, and the gym.
Probable Reasons for Designers Decisions
The VAV system was most likely chosen for the office levels because they are large, open spaces. These systems are also most commonly used in offices buildings because they can control the majority of the conditions affected by HVAC, including temperature, humidity, and carbon dioxide levels (all extremely important in an office setting). VAV systems are very efficient and provide independent temperature controls for different spaces. These systems can be turned off at night to save energy, and easily turned back on during the daytime, or occupied hours. VAV systems are relatively quiet systems, which is important in a building that consists mainly of residential and office space. It is also a reasonable system because of the spaces in the building; the office levels have large, open floor plans and enough room for the duct work required by the VAV system. For this reason, it is logical that the VAV system was not continued through the residential floors. These levels do not have enough space between floors (in the ceiling) for the VAV ductwork, and it is not a realistic system for the residential spaces.
The chosen system for the residential floors is a heat pump system. Heat pumps have been used in residential purposes for centuries because they are one of the most efficient home heating systems available. They provide heat during the cold months, and can be reversed during the hot months to provide cooling. These systems take up much less space than the VAV systems because it is strictly a hydronic system, so there is not the complicated (spacious) ductwork required, just piping. They are a smart choice for the residential floors because each occupant can adjust the temperature to their desire. Another benefit of choosing this system is heat pumps do not generate dry air when heating, which is important when considering humidity levels. Heat pumps are known for generating uniform heating, and are generally quiet systems. A disadvantage of heat pumps is the initial cost can be high, but the FMC Tower is advertizing luxury apartments, leading us to believe the rent will be high enough to cover this cost. Heat pumps are high maintenance systems, which could cause issues in the future. However, all parts of the system will be exposed, unlike other types of heat pump systems, such as those that use the earth as their source (geothermal heat pump) which will make maintenance easier. Overall, this will be an effective system for the FMC residences.
Calculations
The HVAC calculations were estimated using eQUEST. The building was broken into two separate systemes, and run separately through eQUEST, and the results can be seen below. This was done because of a few reasons: the office levels have a different structural system, and therefore a different style floor plan, but most importantly, a different type of HVAC system than the residential floors. eQUEST is only used for general estimates, and therefore it was important we used as many details as we could (including floor plan, height and actual HVAC system) to determine the best possible estimates.
eQuest however does have some limits in it's modeling choices, and the decisions in creating the model probably leads to some inaccuracies. The modeling inputs are listed below:
FMC was seeking LEED certification in their design, the office levels are also equipped with a chilled beam system to combat energy losses due to the large window areas. This is added in the eQuest as chilled water cooling, however there are two heating systems in the offices, coming from both the basement boilers, and electric re-heats on each floor. Because eQuest only has 1 input for heating system, it was decided to use electric resistance since most floors would be more greatly affected by this system.
The residential floors use heat pumps as their main systems, chosen for both user configerability and ease of owner utilities rating. This was modeled in eQuest using DX coils+Pumps.
 Monthly Peak Offices |  Monthly Peak Residences |  Annual Peak Offices |
|---|---|---|
 Annual Peak Residences |  Monthly Energy Consumption Office |  Monthly Energy Consumption Residences |
In terms of lifetime energy use, a general estimate of building energy costs is typically around 2% of build cost per year.
As a result of FMC's LEED certification standards however, FMC may cost significantly less to run per year, though initial costs will also be higher.
A 2% of initial cost estimate for FMC would be around $7,000,000 per year running costs, but this is likely an overestimate based on the previously discussed LEED efficiencies.
Depending on Utilities rates, running costs long term may fluctuate as well.