Commissioning a Geothermal Heat Pump SystemGeothermal Loop Open Loop Open loop takes water from...
Transcript of Commissioning a Geothermal Heat Pump SystemGeothermal Loop Open Loop Open loop takes water from...
Commissioning a Geothermal Heat Pump
System
Matthew Tunnard, LEED®
Horizon Engineering Associates, LLP
Presentation Goals
Describe How a Geothermal Heat Pump System WorksShow a Case Study of a ProjectShow items of Particular Concern to the Cx AuthorityShow the Pros and Cons of the System
How a Geothermal Heat Pump System Works
Geothermal FieldWhere heat is rejected to or captured fromWorks like a cooling tower
Heat PumpA simple air conditioner that can “run in reverse”
Why Use Geothermal
Ground temperature is constant and an excellent heat sinkWater Cooled Electric Heat Pumps can operate more efficiently with a constant condenser/evaporator temperatureThe Earth is a free source of energyThe system has a XXX payback
Geothermal Loop
Open LoopOpen loop takes water from aquifer and pumps it through the heat pumpNeeds very good filtration to capture particulate and keep system operating efficientlyNeed to have a large supply of water availableCan use lake water if code permits• Must worry about biological growth
Geothermal Loop
Closed LoopLoop is buried in the ground in a series of wells based on the heat load.Loop can be placed in a lake or pondSystem needs much less filtration and minimum chemical maintenance once running.Loop must be properly pressure tested before burying.
Heat Pump Operation
General OperationUses energy from the ground in a simple refrigeration cycleCan automatically switch from heating to cooling without operator input
Heat Pump Operation Cooling Mode
Heat Pump Operation Heating Mode
Case Study – Heilmann Middle School
Project Description
150,000 ft2 Middle School in Detroit MichiganGeothermal Loop under football field87 Heat PumpsOpen Protocol control system (Tridium)
HVAC System Description7 Constant Volume Energy Recovery Units (ERU) supplied fresh air make up to the heat pumpsERU’s also exhausted air from the spaces with ducted exhaustHeat pumps would return air from the space and condition it to maintain temperature set pointHP return air would mix with the fresh air make up from the ERU
Project Description Basic Floor Plan
Geothermal Loop – details
Closed systemMade up of vertical wells 600’ deepSpecial PVC PipeTwo main pumps with VFDSide stream filterAuxiliary HeaterWater filled
Geothermal Loop Operation
The pumps were sized for complete redundancyThe buildings boiler provided domestic hot water and also had a supplemental heat exchanger for the geothermal loopVFD’s maintained a constant discharge pressure
Installation Techniques
Geothermal LoopClosed Loop•Not open to air•Pipe is heat fused together•Pressure testing very important
• Pipe stretches a little
Heat Pump - Details
Sequence of OperationUnit would be in Occupied mode during set scheduleIn occupied mode compressor would cycle on/off to maintain space tempIn occupied mode the fan would remain on to provide fresh air make up from the ERU
Installation TechniquesHeat Pumps
Locations• Locate in mechanical room• Build separate closet for HP• Locate above a ceiling
Issues to be considered for location• Access to filters• Access to control valves and strainers• Replacement of compressor• Replacement of complete unit• Noise may be an issue
Commissioning Issues
Access is one of the main concerns with heat pump systems
Filters need to be changedStrainers need to be cleanedFans and compressors need to be servicedThe life of the unit is about 15 years, the entire unit may need to be replaced. This needs to be designed in.
Commissioning Issues
ControlsHeat pumps typically come with self contained unit controlsConnecting the heat pump to the BMS system can be difficult.Various companies “Open Protocol”may not be able to talk to each other
Commissioning Issues
BalancingVery important to ensure that fresh air make up is properly balanced.Transverses of small round ducts may be required to properly balance fresh air.Water balancing is critical to ensure proper loading on units.Lower operating cost
Commissioning Issues
Geothermal LoopThis is the heart of the systemThe pumps must always be running• Water must be available whenever a heat
pump starts
Should provide 3-way valves at the end of mains to always provide flow for the pumps• Attempted to use controls to maintain
minimum flow--very difficult to achieve
Pros and Cons
ProsIndependent unitsExcellent individual control• South side rooms can be in cooling while
north side are in heating.
Redundancy• Loss of a heat pump does not affect any
other spaces. No central chiller or boiler to fail.
Pros and Cons
ConsGetting the controls to work togetherGeothermal loop may restrict future site expansion• Can’t build a building on top of the loop
Initial cost of the geothermal loopReplacement of the heat pumps in 15 years.
Pros and Cons
Geothermal LoopOpen vs. Closed Loop• Open uses much less space, closed can’t be
built upon• Closed is much less susceptible to foreign
matter clogging parts• Closed has less impact on aquifers
Summary
Very simple systemVery reliableClosed Geothermal loop is virtually maintenance freeExcellent space controlNeeds to be planned for maintenance/replacementControls interface is critical