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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.
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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.
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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.
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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.
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