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The Hybrid HVAC System, Part I: Concepts and working systems
The Hybrid HVAC System, Part II : Typical s

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Shown below in Figure 1 and  Figure 2 are concept hybrid HVAC system schematics where a fan/coil is integrated with a heat recovery ventilator in a dehumidified mechanical room closet; and are what we believe to be one of the transitional solution between the past and the future in HVAC. Before anyone panics, we know the mechanical closet idea is not new and is adapted here from the work of Armin Rudd from Building Science Corporation; nor is the integration of an HRV/ERV core with a fan/coil, furnace or boiler new as these products are readily available from manufacturers (see below for examples). We just don't know of anyone as yet (summer 2011) who has specifically combined these elements. If so - forgive us and tell us how its working.

The principle: hydronic fan/coil along with say a radiant floor cooling and heating system would be served from a storage tank connected to a solar or geo system or connected to a community based district cooling and heating energy system. Dehumidification of space air (if required) would occur within the closet itself. Humidification (if required) would be done in the downstream air plenum using steam.


Figure 1. Type 1 Hybrid - Single fan HRV/ERV unit w/ or w/o humidity control and optional floor cooling and heating

Figure 2. Type 2 Hybrid - Multi-fan HRV/ERV unit w/ or w/o humidity control and optional floor cooling and heating
Off the shelf equipment: Integrated systems

Figure 3. Condensing boiler integrated with HRV core, brazed plate heat exchanger for domestic water heater and optional radiant floor heating.

Figure 4. Above left image is an integrated fan/coil with a heat recovery core. Right image is the inside view from the installation in Figure 5.


Figure 5. Above example of a traditional hybrid. Shown are off-the-shelf fan/coils with HRV cores and a wall mount condensing boiler for domestic water and radiant floor heating.

Packaged Control Appliances: Hydronics

Figure 6. Above is an off-the-shelf factory assembled and electrically certified hydronic control appliance with electric boiler (shown as item 4 in schematic below) - set up for radiant floor heating. This same type of panel could also serve the fan/coils in addition to the radiant system.

The solar hybrid

Figure 7. We see the future in mechanical system to be some form of a combination of the types of equipment above -integrated into a mechanical room closet and served by a geo* and solar thermal system for base loads with electric or gas fluid heaters for peak loads. Which means a whole bunch of things like - if you do "air only" learn hydronics so you can deal with solar and geo thermal and if you do "hydronics only" learn air so you can do dehumidification, deodorization and decontamination of the ventilation air.

*Geo as in not to be confused with a ground source heat pump, but a direct connect ground loop system sans compression.

See: The Hybrid HVAC System, Part II : Typical schematics

Suggest study:

Dedicated outdoor air systems (DOAS)
The Hybrid HVAC System, Part II : Typical schematics

Additional reading:

  1. Lstiburek, J., Residential Ventilation and Latent Loads, ASHRAE Journal, April 2002

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