Leonard Palmer

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Pipecycle_Experiment

Heat recovery + radiative cooling

Spring 2024
Grinham Research Group
Harvard GSD+SEAS
Building systems have traditionally been separated from architectural design, existing as add-ons to a building. The conceptual folly Pipecycle integrates radiant-based thermally active building systems into architectural spacemaking with a closed-loop hydronic pipe system that embodies various levels of surface emissivity, which strategically absorbs, rejects, or emits heat, thereby creating distinct thermal spaces. Outdoor testing of a proof-of-concept prototype and analytical model demonstrate surface emissivity control with significant heat recovery from black-coated pipes and cooling potential from PVDF-coated pipes, showing potential for large-scale energy exchange using radiant systems. 

Publication: 
Palmer, L., Naginski, E., La, G., Grinham, J. (2025). Pipecycle: A Heated Exchange Between Systems and Space-Making. In: Berardi, U. (eds) Multiphysics and Multiscale Building Physics. IABP 2024. Lecture Notes in Civil Engineering, vol 554. Springer, Singapore. https://doi.org/10.1007/978-981-97-8313-7_25
Presented at:
- 9th Int’l Building Physics Conference, Toronto Metropolitan University (July 2024).
- Material Time Symposium, Harvard GSD (April 2024).

Conceptual folly Pipecycle uses the geometry of the Möbius strip to seamlessly integrate radiant systems into architectural space making. The folly consistes of pipes that vary in surface emissivity to absorb, reject or emit heat to its surroundings.
Harnessing the cooling potential of the cold water in an existing underground reservoir, Pipecycle creates a cool zone on one side, by having the low emissivity polished aluminum surface facing outward. The black side of the pipes then flip outward to absorb solar radiation from the south, with its black, high emissivity side. Once the water is heated up, it reaches the opposite side to heat the space, eventually returning to the reservoir below.
The pipes have different levels of emissivity in the NIR and MIR, which controlls the radiative heat exchange with its surroundings and the sky.
Initial indoor lab experiment tested polar opposite sides of surface emissivity: fully polished aluminum (low emissivity), half and half, and fully matte black (high emissivity). The experiment flowed warm water through each pipe, and recorded the rate of decline in temperature once the water was shut off.
The thermal image intuitively and clearly shows how the black aluminum pipe on top is emitting more heat compared to the polished aluminum pipe below.
To explore the potentials of radiative sky cooling in this system, a set of pipes were coated with a porous polymer made with PVDF. The microscale air bubbles are created as the acetone evaporates off, creating a porous structure reflects sunlight, while emitting heat through the atmospheric window. Left: custom jig to coat the pipes with the porous polymer. Right: Diagram taken from Mandal et al., “Hierarchically porous polymer coatings for highly efficient passive daytime radiative cooling,” Science, vol. 362, no. 6412, pp. 315-319, Oct. 2018.
Six polished putipurpose 6061 aluminum round pipes (1/2” ID, 3/4”OD, 12” length) were treated with different surface coatings that capture polar ends of emissivity. Three samples of PVDF were fabricated due to variability in thickness of the polymer coating. Each pipe was inserted into a CNC-milled polystyrene insulation shell faced with aluminum foil to provide equal radiant views to the environment and to prevent radiative exchange between the samples. The experimental system was topped with 3/16” thick foam core with rectangular holes exposing 11 1/2” length of each pipe. 0.0009" thick polyethylene film with lab-measured IR transparency of 85% sealed the system to prevent convective heat exchange with the environment.
Thermocouples were placed inside at the inlet and outlet, as well as at the outer surface of each pipe. The mass flow rates of the water (g/s) were recorded and calibrated to ensure uniformity across the six samples. 
Experiements were conducted outdoors in March and April 2024 in Cambridge, MA. The system was connected to a water pump that fed tepid water (20C) in an open loop for 1-2h. A pyranometer recorded the solar irradiance.
Thermocouples were connected to data loggers on the back side of the system.
A sample of the data of the resulting heat flux for the six cases from one test day. The figure shows multiple heat exchange conditions in an environment with an average outdoor temperature of 15 °C and a clear sky with an average NIR heat flux of 516 W/m2. The black pipe experiences an average heat gain of 367 W/m2, or about 71% energy recovery of the available solar energy. PVDF samples 1 and 2 averaged − 89 W/m2 of cooling. The aluminum pipe’s heat flux is 96 W/m2, or a gain of 18%. The half system showed an average heat flux of 104 W/m2.
This chart showsthe resulting surface temperature when the water flow is turned off and the inlet and outlet valves are closed.
Rare data was collected during the solar eclipse on April 8, 2024 - showing the highly emissive black pipe dropping faster in surface temperature than the low emissivity polished aluminum pipe while the sun was eclipsed. 
A theoretical design of a scaled up experiment of this radiant-based system, providing cooling for the occupant below. 
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