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GREEN HVAC Mixed Modes
Combining Slab and Air modes to obtain fine control.

This page describes the various mixed Slab and Air modes of my GREEN HVAC system.   In this case, GREEN is an acronym for:  Geothermal, Radiant, Efficient, Energy-Network and it describes a Heating, Ventilation and Air Conditioning (HVAC) system that I am designing for my new home.  Before reading this page, you should read my HVAC and HVAC Modes pages to get an understanding of the system components, and the basic primary and secondary operational modes that are being combined on this page.

To Recap: My GREEN HVAC system has four primary operational modes used to regulate the thermal slab temperature, and four secondary modes used to control air temperature and humidity.  Depending on several environmental factors, the Slab and Air operational modes will be chosen to achieve the desired human comfort level while utilizing the least possible energy. Sixteen different mixed modes are available.  A few of these are not very practical, but they have been listed anyway.

The tables below groups the mixed modes by their primary (slab) mode.

SHAH - Slab Heat : Air Heat.
This is the most severe and lest efficient of all the heating modes.  This mode would be used in extreme cold conditions only. Active slab and air heating is being utilized.  If the air heating coils are placed in series, before the slab loops in the energy circuit, the air temperature will be higher than the slab temp.  Alternatively the air coils could be after the slab coils, or in parallel with them.

SHAD - Slab Heat : Air Ground.
This mode is raising the slab temperature, while pre-conditioning the incoming air with ground water. This mode is useful if the incoming air temperature is greatly below the earth temperature.  In this case the ground water is passively heating the incoming.

SHAD - Slab Heat : Air Dehumidification.
This mode raises the slab temperature, while actively dehumidifying the incoming air. This mode would be useful in cool, damp weather.

SHAC - Slab Heat : Air Cool.
This unlikely mode would be used if the slab temperature is below the desired internal temperature, but the incoming air temp is above the desired temp.  This could be caused by a sudden hot front after many cooler days.

 

SMAH - Slab Mixing : Air Heat.
This is mode distributes the slab energy (temperature) while actively heated the incoming air.  This mode would be useful on cold but sunny mornings when the slab temperature is rising slowly, but the incoming air is still too cold after passing through the ERV.  This condition would not prevail for long on sunny days.

  

SMAD - Slab Mixing : Air Dehumidification.
This is mode distributes the slab energy (temperature) while providing active air dehumidification.  This mode is used when the passive solar design is capable of maintaining a suitable slab temperature, but the incoming air is too moist to be healthy.

  

SMAG - Slab Mixing : Air Ground.
This is mode distributes the slab energy (temperature) while preconditioning incoming air with ground water.  Although drawn here as a cooling function, this mode could be used to cool hot air, or heat frigid air.

  

SMAC - Slab Mixing : Air Cooling.
This is mode distributes the slab energy (temperature) while actively cooling the incoming air.  This mode is useful if the slab is at a reasonable temperature but the incoming air is extremely hot and humid.

  

SGAH -  Slab Ground : Air Heat.
This is an unlikely mode since the only reason we would be grounding the slab would be to cool it, and therefore it's unlikely that we would be heating the air.  However, it is possible that this mode may be required during a rapid drop of outside air temperature. 

SGAD Slab Ground : Air Dehumidify.
This mode cools the slab using ground water, and actively dehumidifies the incoming air without dropping it's temperature greatly. This mode best suites mild temperatures with moderate to high humidity.  

  

SGAG Slab Ground : Air Ground.
This mode cools the slab and incoming air using ground water.  This is a super efficient mode that can be used for mild summer temperatures. 

SGAC Slab Ground : Air Cool.
This mode cools the slab ground water, and cools the incoming air using the heat pump. This mode is great for for warm days with high humidity, where the major cooling load is overcoming the latent energy load of dehumidification.   Note that the slab is fed directly from the ground loop.  The heat pump dumps directly back into the earth.

SCAH Slab Cool : Air Heat.
This mode is extremely unlikely since active slab cooling would only be used is when there is a very high thermal gain due to external temperature and solar radiation (sunlight).  Under this condition it is unlikely that air heating would also be required.

SCAD Slab Cool : Air Dehumidify.
This mode is actively cools the slab while dehumidifying the incoming air without lowering it's temperature.  This mode is appropriate very sunny days with mild temperatures and high humidity.

SCAG Slab Cool : Air Ground.
This mode is actively cools the slab while cooling the air with ground water.  This mode is appropriate very sunny days with mild temperatures and high humidity.

SCAC Slab Cool : Air Cool.
This is the most severe, and least efficient of all cooling modes.  This mode would only be used in the most temperature or humidity environments.  If the air cooling coils are placed in series, before the slab loops in the energy circuit, the air temperature will be lower than the slab temp.  Alternatively the air coils could be after the slab coils, or in parallel with them.