This document outlines the design and implementation of the Vertical Hydronic Recovery Stack (VHRS), a high-efficiency climate control and heat recovery system. The VHRS is designed to leverage the "Stack Effect" and mechanical hydronic modules to provide optimal thermal management for a 4,000 sq. ft. structure.
- Size: Optimized for a 4,000 sq. ft. structure (Basement, First Floor, Conditioned Attic).
- Role: Primary climate control, dehumidification, and heat recovery system.
- Primary Energy Medium: Propylene Glycol/Water hydronic loop.
- Efficiency Goal: 25–35% reduction in total utility load compared to conventional HVAC.
- Implementation Phase: phase-2
The system reverses airflow and thermodynamic roles based on the season to maximize the Coefficient of Performance (COP).
- Airflow: Intake at Basement → Exhaust at Attic Stack.
- Thermal Logic:
- Basement Module: Acts as the Evaporator, cooling and dehumidifying incoming air.
- Attic Module: Acts as the Condenser, rejecting household heat into the exhaust stream.
- Advantage: Utilizes ground-tempered basement air to "pre-cool" intake and flushes the hottest attic air out through the roof.
- Airflow: Intake at Attic Stack → Exhaust at Basement.
- Thermal Logic:
- Attic Module: Acts as the Condenser, heating incoming air using solar gain from the conditioned attic.
- Basement Module: Acts as the Evaporator, "scavenging" remaining heat from the air before exhaustion.
- Advantage: Pushes heat to the lowest point of the house, allowing natural convection to warm upper floors while utilizing the basement slab as a thermal battery.
- The Stack: Insulated double-wall spiral ducting (12"+ diameter) extending from the basement to 5ft above the roofline.
- Fan Modules: Identical units in the Attic and Basement featuring Reversible EC Fans (High-Static/Low-Velocity) for quiet, efficient operation.
- Fluid: Propylene Glycol/Water mix to prevent freezing.
- Plumbing: PEX or Copper lines connecting floors, eliminating refrigerant oil-return issues associated with long vertical rises.
- Pump: Variable-speed circulator (e.g., Grundfos/Taco).
- Compressor: Variable-speed Inverter DX unit.
- Heat Exchangers: Brazed-plate or coaxial exchangers interfacing the DX loop with the Hydronic loop.
- DHW Integration: A 3-way diverting valve on the "Hot Side" prioritizes heating domestic hot water.
- Summer Benefit: Provides "free" hot water by using the tank as a heat sink for the cooling cycle.
The system is managed by a custom controller (PLC or ESP32) focusing on:
- Psychrometric Throttling: Throttles the compressor based on Dry-Bulb and Wet-Bulb data to prevent coil frosting and optimize latent heat removal.
- Pressure Balancing: Synchronizes fan speeds to maintain neutral pressure and prevent backdrafting.
- Energy Performance: Estimated at ~7,300 kWh/year vs. ~11,000 kWh/year for conventional systems.
| Challenge |
Solution |
| Refrigerant Oil Return |
Use a Hydronic Loop between floors; keep DX components localized. |
| Condensation in Basement |
Intake-side dehumidification via evaporator coil + floor drainage. |
| Attic Air Quality |
Conditioned/clean attic space + MERV 13 filtration at stack intake. |
| Freezing Risk |
Glycol-based fluid + compressor throttling based on dew point. |
| Static Pressure |
Oversized ducting (12"+) to maintain low-velocity, quiet airflow. |
- Hardware (Compressor, Fans, HX, Pump): ~$12,000 - $18,000
- Ducting & Plumbing (Spiral Duct, PEX/Copper): ~$4,000 - $6,000
- Controls & Sensors (PLC/ESP32, Psychrometric Sensors): ~$1,500 - $2,500
- Estimated Total Gross Cost: $17,500 - $26,500
- Structural Integration: Install the vertical stack during the framing phase of phase-2.
- Hydronic Plumbing: Run PEX/Copper lines between the basement and attic modules.
- Module Installation: Mount the fan and heat exchanger modules in the basement and attic.
- DX Engine Setup: Install the inverter compressor and interface with the hydronic loop.
- Controller Deployment: Install sensors and the PLC/ESP32 control system.
- Commissioning: Perform pressure testing, fluid charging, and control logic calibration.
¶ Man-hours for Construction and Operation
- Stack & Ducting Installation: ~60-80 hours
- Hydronic Plumbing & Pump Setup: ~40-60 hours
- Module & Compressor Installation: ~80-100 hours
- Control System & Sensor Wiring: ~40-60 hours
- Total Estimated Construction Man-hours: ~220-300 hours
- Filter Changes & Visual Inspection: ~10-15 hours/year
- System Monitoring & Optimization: ~5-10 hours/year
- Total Estimated Operational Man-hours: ~15-25 hours/year
¶ Maintenance Financial Report (Annual Estimate)
- MERV 13 Filters: ~$200 - $400
- Pump/Valve Maintenance Fund: ~$150 - $300
- Glycol Testing/Top-up: ~$50 - $100
- Total Estimated Annual Maintenance Cost: ~$400 - $800
¶ Maintenance
- Filter Replacement: Quarterly replacement of MERV 13 filters.
- Fluid Check: Annual check of glycol concentration and pH levels.
- Fan Inspection: Bi-annual inspection of EC fans for debris or wear.
- "Modern Hydronic Heating" by John Siegenthaler: The definitive guide to hydronic system design.
- ASHRAE Psychrometrics Resources: For understanding latent vs. sensible heat management.
- Inverter DX Technology Documentation: Technical specs from manufacturers like Daikin or Mitsubishi.