Oregon Water to water heat pump install

Discussion in 'Geothermal Heat Pump Testimonials' started by wing, Aug 29, 2019.

  1. wing

    wing Member

    So on with the story. Details of constructing the six loop, 4200 foot horizontal loop field for this project were previously posted in the appropriate ‘loop field’ section of this forum (‘My most awesome horizontal closed loop’)

    The two inch header lines from the loop field were crossed over to 1 1/4 inch copper in the crawl space. Very standard using off the shelf materials.


    Next the HVAC contractor started the flow center and heat pump piping in 1 1/4 copper according to design specifications. The flow center is non pressurized using a Grundfos Magna Geo 32-140 variable speed in series with a fixed speed Grundfos 26-99. Control of the two pumps is accomplished with either a flowmeter or with differential temperature sensors across the heat pump supply and return. A manual flow center current mode is also available. The Grundfos flowmeter looks like a potential weak link with rather substantial head loss so I went ahead and added a flowmeter by pass. Reinforced steel flex hoses are used liberally throughout to dampen vibration as are brass unions to facilitate maintenance or replacement.

    Sensor points have been added to both the supply and load loops to allow continuous system monitoring and data logging:

    Loop supply temperature
    Loop return temperature
    Delta Pressure across the heat pump supply (GPM flow rate)
    Load supply temperature
    Load return temperature
    Delta Pressure across the heat pump load (GPM flow rate)
    Current meter to the heat pump
    Current meter to electric resistance heater in DHW tank


    Eventually all this will tie in to a main distribution panel downstream of the heat pump either directly or via the buffer tanks. For the main distribution panel I went with Eagle Mountain who build a customized distribution panel that is plug and play including the control systems. They do nice work.

    Distribution panel pumps have the following assignments:

    Pump 1 - Domestic hot water with priority override
    Pump 2 - Main water to air handler (cooling or heat mode)
    Pump 3 - Tower water to air handler (cooling or heat mode)
    Pump 4 - Manifold 1 in floor heat (all in floor heat is 1/2 inch hePex embedded in 1 1/2 gypcrete)
    Pump 5 - Manifold 2 in floor heat
    Pump 6 - Manifold 3,4,5 in floor heat
    Pump 7 - Garage floor cement slab.

    The in floor loops have all been pressure tested / filled and flushed with pure water. The hePex piping runs from the in floor manifolds to the main distribution panel.


    Just a look at one of the five in floor manifolds scattered throughout the residence providing a ‘highly zoned’ in floor heat experience. Manifold control is via thermostat with floor slab sensors.


    Over the next two weeks plan on fill and flush the loop field using a flush cart, hooking up the heat pump itself and installing the buffer tanks.
  2. wing

    wing Member


    All the heat pump piping is now complete. The differential pressure sensor points are located at the heat pump elbow ports (the load side ports are marked with a P) and source / load EWT and LWT temperature probes are scattered at different points of the piping arrangement. The sensor sandwiched between the two short pieces of rubber hose is a Grundfos flow meter. Note the flow meter can be bypassed by using the ball valves. Also noteable is the heat pump bypass for isolating the ground loop.

    Design ground loop fluid capacity is 205 gallons. Using a 1/2 horsepower transfer pump, I was able to put away 160 gallons into the loop. The balance is air in one or more of the loops. This will be flushed out when the system is hooked up to a 2 horsepower flush cart.
  3. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    looks beautiful
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Enlighten us a bit with some more design details, so we can understand your rational and learn something here.

    1) What model and size water-water heat pump do you have?
    2) Why a flow center with a variable and constant speed pump?
    3) What model numbers for the distribution pumps?
    4) Why a flowmeter?
    5) Why in floor temp sensors?
    6) where is your load water going coming out of the heat pump? Buffer tank? direct to the zones?
  5. wing

    wing Member

    1) What model and size water-water heat pump do you have?

    The heat pump is a 5 ton Terra Therm THA-060 single stage water to water. Single stage was chosen to reduce system complexity in this new construction house in rural Oregon with limited access to repair technicians.

    Radiant floor heating via hePex tubing embedded in 1.5 inches of gypcrete delivers heating to the first and second floors.Two air handlers located in the ground floor mechanical room and the third floor provide cooling and auxiliary heat. Manual J heat load has been calculated at 6 tons so the system is slightly under designed with electrical resistance heating elements incorporated in the air handlers for extreme conditions occasionally encountered.

    Provision has been made for the system to provide hot water via the heat pump and an indirect heated water tank (with electrical back up). Although the Terra Therm heat pump has a de-superheater, it has not been utilized in this initial design.

    Manual J, ducting and radiant floor design was performed by Enser Consulting, a professional consultant firm out of Lakewood, Colorado.

    terra therm 5t.png

    2) Why a flow center with a variable and constant speed pump?

    The closed loop implemented for this project consists of quantity six 700 foot loops of 0.75 inch HDPE pipe connected to an outside header and then back to crawl space via 250 feet (one way) of 2 inch HDPE (see my post in the appropriate section of this forum detailing the closed loop install).

    The non pressurized flow center is a Geo Flow NPV2 model with series Grundfos Magna GEO 32-140 and UPS26-99 fixed speed pumps. The pressure drop curve for the heat pump / closed loop system is shown below along with the pump curves for the NPV2 pumps.

    system design.jpg

    The 15 gpm design point is comfortably within the capacity of a single Magna GEO 32-140 variable speed pump.

    There will be some power savings using the variable speed at a 15 gpm flow rate. Not much but some.

    Provision has been made in the heat pump piping to add an additional 2 ton heat pump in parallel to the 5 ton for dedicated hot water heating if so desired. Certainly the loop field is capable of handling additional load. With a second heat pump and 21 gpm flow rate the NPV2 flow center controller will then activate the fixed speed UPS 26-99 to handle the base load and float the variable speed pump to handle the volume requirements.

    So the short answer is the two pumps in series solution was selected to future proof an additional heat pump installation as well as minimize power requirements.

    3) What model numbers for the distribution pumps?

    The pumps used on the Eagle Mountain distribution panel are:

    1. Load Pump- Grundfos UPS43-100F 3-Speed High Flow SuperBrute Flanged Circulator Pump, 230V
    2. Indirect Water Heater - Grundfos 15-58FC Fixed Speed
    3. Air Handler 1 - Grundfos 15-58FC Fixed Speed
    4. Air Handler 2 - Grundfos 15-58FC Fixed Speed
    5. Caleffi Radiant Manifold #1 - Grundfos Alpha2 Variable Speed in constant pressure mode
    6. Caleffi Radiant Manifold #2 - Grundfos Alpha2 Variable Speed in constant pressure mode
    7. Caleffi Radiant Manifold #3, #4, #5 - Grundfos Alpha2 Variable Speed in constant pressure mode
    8. Garage Slab - Grundfos 15-58FC Fixed Speed

    Copy of pump description2.jpg

    4) Why a flowmeter?

    The Geoflow NPV2 flow center with variable speed pump has several control modes to continuously alter pump speed to deliver a specific or optimum gpm to the heat pump.

    The modes are flowmeter , differential temperature across the heat pump supply and return, and fixed current. The flowmeter, temperature sensors and flow center control box are included with the NPV2 package.

    While the this Grundfos flowmeter will be useful in the initial startup and for troubleshooting, I am frankly leery of how well it will work in day to day operations. For starters it will increase the heat pump supply pressure drop. And it just looks like a weak link in the setup. Accordingly, a bypass to the flowmeter has been included.


    Provision has also been made for differential pressure sensors across the heat pump supply and load ports so strictly speaking I dont need the flowmeter except as one of the control modes for the NPV2 flow center.

    5) Why in floor temp sensors?

    There are a total of seventeen Tekmar 532 thermostats scattered throughout the home to allow for a 'highly zoned' radiant floor experience. The Tekmar has both air and floor slab sensors. Floor slab sensors were inserted inside pex sleeves prior to the gypcrete pour.

    Floor and Air Temperature

    If the air sensor is turned on and a floor sensor is connected, the thermostat will maintain the desired air temperature as well as a minimum floor temperature. This operation is recommended for areas with large windows that allow the sun to shine into a room and keep it warm without the need for heating. This can allow the floors to cool off during the afternoon. When the sun goes down, it can take a long time for the floors to get warm again. This may cause the room to cool off too much in the early evening. A floor minimum setting can help with this condition by maintaining a floor minimum temperature. Keep in mind the floor minimum temperature will override the air temperature, and if set too high, may overheat the room.

    This operation is also recommended for rooms with hardwood floors. Setting floor minimum and maximum temperatures is a way of enhancing the comfort of the living space while protecting floor coverings.

    In this case, the home qualifies on both counts - there is a much glazing on the south and west sides of the home (west glazing to take advantage of territorial views) and the majority of the floor covering is engineered wood. Note - picture of home is oriented to show the south aspect.

    DJI_0180 edit 1.jpg

    6) where is your load water going coming out of the heat pump? Buffer tank? direct to the zones?

    Indeed it has been demonstrated by geothermal professionals that delivery of the hottest / coldest load water possible maximizes the efficiency of heat pump systems. Accordingly, the heat pump load piping connects directly to the distribution panel and bypasses the buffer tanks. The piping arrangement also allows minor heating / cooling calls to be handled by the buffer tanks without activating the heat pump, thus reducing short cycling.

    Panel Piping .jpg
    Last edited: Oct 9, 2019 at 6:01 PM

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