PROJECT: Dolwick Drive Office Projects
In response to the growing demand for prime office space in the Greater Cincinnati Tri-State area Corporex embarked on an ambitious building project to renovate a 230,000 square foot warehouse. The vacant warehouse sits in close proximity to the Cincinnati / Northern Kentucky International Airport providing an ideal location for business offices.
Corporex teamed up with Commercial HVAC to design and install the HVAC systems for this renovation. The existing single story warehouse was converted to a 2-story office space by the addition of a complete second floor slab. The deck to deck heights were very low as the existing roof structure was not raised to accommodate the second floor.
A unique feature of this long building is the two-story atrium with barrel skylight along with interior courtyards. It’s rare for new office building construction to incorporate such design features to provide natural lighting much less in a renovation project such as this.
Early in the design phase it became apparent that the existing “warehouse” metal roof was designed for minimal loading and would not be adequate to accommodate roof mounted HVAC equipment. In addition, because of the low ceiling height, installation of an all air system with larger trunk ducts would be problematic. An HVAC system using smaller hydronic piping would probably be the best choice, although it would be higher first cost.
Several HVAC system options were explored including DX/VAV, chilled water, and water-source heat pumps. Based on the owner’s desire to maintain flexibility in the layout to accommodate future tenant changes and provide the best zoning possible the Water Source Heat Pump system was chosen.
No sooner had the design team begun working on the construction documents when Corporex signed its first tenant The GAP wanted to lease 50,000 sq.ft. of office space (almost a quarter of the building), but with the stipulation they have occupancy in less than 12 weeks! Obviously the design and construction schedule had to be compressed.
Because of the design of a water-source heat pump system there aren’t any “shortcuts” that can be taken compared to other system designs. The entire hydronic system including piping, boilers, cooling towers, and controls along with the make-up air systems needed to be fully functional to accommodate the first tenant.
During the design phase Commercial HVAC became aware of yet another pre-existing condition that required a creative solution. Once the existing roofing structure was modified to accommodate the interior courtyards and skylight there was a concern regarding the additional weight requirements that would be imposed by the new HVAC system.
Commercial HVAC presented an option to develop a more efficient heat pump system utilizing a Taco LoadMatch® single pipe instead of the traditional 2-pipe system. Working closely with Taco and their local representatives, Commercial HVAC was able to eliminate almost half of the piping and reduced the imposed weight to the structure by approximately 50%.
In addition, because of fewer materials to install, the system could be installed quicker, meeting the now compressed construction schedule. The system is also self balancing which reduced the start-up time and elimination of call backs for “tweaking” balance valves to make the occupants comfortable.
The system is also more efficient. By the elimination of balance valves, control valves and some pipe, because the system is a direct return, the system has a lower pump head and lower installed horsepower. In addition, the flow in the secondary circuits is variable volume, with constant volume circulators, because the circulators are operated to match the load. The electrical consumption for pumping is therefore less than a conventional 2 pipe system.
Another advantage of the single pipe system, particularly on this project, is the ease of tenant finish. The single pipe system carries the full capacity of the building or area that it serves. As a result, a heat pump unit can be added anywhere in the piping system without regards to location. With diversity, if a typical heat pump unit does not use the available btu’s in the pipe, than they are available to any unit downstream and are not bypassed or “lost” to the return pipe in a 2 pipe system.
Using the Taco LoadMatch® system special “Twin Tee” fittings were used along with in-line circulators for each heat pump. A single Twin Tee replaces 2 tees in a conventional system. The Twin Tees again reduced the amount of materials and decreased installation time for the project.
The small secondary circulators were sized to circulate water through the heat pumps and the associated secondary piping from the main line. The primary system pumps were reduced in size due to the reduced head on the primary loop.
The system design is “similar” to the traditional water-source heat pump design, but instead of circulating excess fluid through a two pipe system, the system takes advantage of diversity, and the heat pumps were selected based on a blended temperature. Using the blended temperature serves a heat pump system well even at peak load conditions.
The boilers in the system are Parker indirect fired WH series. In an indirect fired boiler the colder heat pump loop water does not come into contact with the high-temperature furnace or into contact with the flue gas at all. This “indirect-fired” process virtually eliminates the problems of rust and corrosion, as well as scaling, that all direct-fired boilers would encounter in a heat pump system.
Because the primary side of the boiler remains at a steady uniform temperature, it not only results in high combustion efficiency and lower fuel consumption, it provides excellent system temperature control, preventing nuisance cold water lock-outs of heat pump units. System start up went smooth with no problems and we’re happy to report that the first
tenant moved in on time and have not registered any complaints about the HVAC system.
Due to the compressed construction schedule, this one-pipe Taco LoadMatch® system
is the first operational system of its’ kind in the Tri-State region as well as the largest.
SCOPE OF WORK