building type: A Minnesota Condominium Association
Project Team: GITTLEMAN CONSTRUCTION & MAINTENANCE (GCM) – PLUMBING DIVISION.
QUESTIONS & SOLUTIONS ENGINEERING, INC.
GITTLEMAN EXPERTISE: Consulting // Plumbing services // Plumbing installation
SPECIFICS OF THIS PROJECT:
LaRive had a program of replacing older and failed heat pumps with new, similar, yet more efficient units. During peak summer conditions, the common areas were suffering from uncomfortable levels of humidity. When Gittleman was brought in to consult, we suspected the heat pumps were oversized and not running in cooling mode long enough to adequately dehumidify the air. Questions & Solutions, Inc. performed a load calculation on the common areas and determined the heat pumps were nearly twice as large as necessary. Gittleman installed a new type of heat pump that was half the size of the existing units. The new heat pumps feature “hot gas re-heat,” which takes readings from the space temperature thermostat and a humidistat. In cooling mode, the system cools to the desired set point. In the event the humidistat is not satisfied, the system continues to cool (sub-cooling) to remove humidity and then use the hot refrigerant gas to reheat the air to a comfortable discharge temperature to prevent overcooling the space. The new system actively controls humidity levels in the space while reducing the load on the core loop water. While the hot gas re-heat heat pumps are approximately 20% more expensive than the larger, direct replacements, the solution effectively addressed the common area humidity discomfort and helped mitigate building envelope issues such as condensation and infiltration.
PROJECT FACTS: LaRive is a 30-year-old, 27-story condominium high-rise complex. Heating and cooling of the building is accomplished by individual heat pumps in the residences and common areas. Heat is transferred to and from the heat pumps by means of a core water loop supplied by a privately owned central plant.