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GREEN HVAC
Using an Energy Network to overcome conventional wisdom.

This page describes the various operating modes of my GREEN HVAC system.  Here, the word GREEN does not take on any of it's typical meanings.  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.  The keywords apply as follows:

Geothermal because utilizing a Geothermal Exchange earth loop is key to the energy efficient operation of the system.
Radiant because the primary heating and cooling action is achieved through radiant temperature equalization.
Efficient because the year-round heating and cooling configurations of this system permit all the components to operate at their maximum efficiency.
Energy-Network because all the active energy transfers in the system are achieved through a switched network of  water pipes. 

This page describes the two categories of  operational modes of  the system, and how the network of interconnecting water pipes must be switched to achieve each mode.  The letter codes of the specific circuits are shown below. The components for schematic below are described on my HVAC page

My GREEN HVAC system has four primary operational modes, and four secondary modes.  The primary (predominant) modes relate to thermal slab temperature control, and the secondary modes relate to air temperature and humidity control.  Depending on several environmental factors, the primary and secondary operational modes will be chosen to achieve the desired human comfort level while utilizing the least possible energy.

For clarity, the distinct primary and secondary configurations are illustrated below.  On the Mixed Modes page, the various combinations of these modes are described. At any point in time, only one primary mode and one secondary mode can be operational.

The four primary Slab modes are designated SH, SM, SG & SC, and are described below.

SH SH is short for Slab Heat, and is used to heat the slab floor.  This Active Heating mode is required when the incoming solar radiation (sunlight) is insufficient to produce a slab temperature required to maintain the desired human comfort level.  The actual desired slab temperature will depend on several factors, such as current thermostat setting (daytime or nighttime setback), outside temperature, time of day and other heat sources.

One circuit connects the Ground loop (K) to the Heat Pump Source (Ls).  The other circuit connects the Heat Pump Delivery (Ld) to the Radiant Slab distribution Manifold (D).   By selectively turning the circulating water on and off in different slab loops (J), varying degrees of heating can be achieved in different house zones. 

When the heat pump operates, it transfers heat from the constant temperature ground source to the slab floor with a 300-400% efficiency.  

SM SM is short for Slab Mixing and is used to produce a homogeneous (evenly distributed) slab temperature.  This Passive mode is required when localized solar radiation causes spot heating of the slab.  Since solar heating will only occur at the exposed South side of the slab, unless some means is used to distribute the heat energy throughout the slab, localized hot spots will always occur.

A single circuit is used to circulate water through the entire slab.  Water from the individual slab loops (J) is re-combined and mixed each time it passes through the Manifold (D).  Since water has a high thermal capacity, this efficiently equalizes the slab temperature through forced convection.

Only a fractional horsepower (300-500W) pump is required to achieve this mode.

SG SG is short for Slab Ground, and is used to cool the slab floor at a moderate rate.  This Passive Cooling mode is extremely efficient, but slower than SC. A possible use for this mode is to drop the temperature of the slab overnight, after an intense solar day.  Alternatively, this mode may provide sufficient cooling on a spring or fall day.  

A single circuit is used to circulate water between the Ground Loop (K) and the slab, via the Manifold (D).  The closed water circuit acts as a thermal bridge between the slab and the deep earth.  By selectively turning the circulating water on and off in different slab loops (J), varying degrees of cooling can be achieved in different house zones. 

Only a fractional horsepower (300-500W) pump is required to achieve this mode.

SC SC is short for Slab Cooling, and is used to rapidly cool the slab floor.  This Active Cooling mode is required when the SG mode is not capable of maintaining the slab temperature within the desired range on a hot sunny day.

One circuit connects the Slab Loop Manifold (H) to the Heat Pump Source (Ls). The other circuit connects the Heat Pump Delivery (Ld) to the Ground loop (K).   By selectively turning the circulating water on and off in different slab loops (J), varying degrees of cooling can be achieved in different house zones.

When the heat pump operates, it transfers heat from the Slab to the constant temperature ground sink with a 300-400% efficiency.  

The four secondary Air modes are designated AH, AD, AG & AC, and are described below.

AH AH is short for Air Heat, and is used to preheat incoming air.  This Active Heating mode is only used if the incoming air temperature is too low after leaving the Energy Recovery Ventilator (B).  In winter, outside air should already be preheated on passing through the ERV.  If for some reason this is not the case,  AH can be used to further boost the air temp to eliminate cold drafts.

One circuit connects the Ground loop (K) to the Heat Pump Source (Ls).  The other circuit connects the Heat Pump Delivery (Ld) to the Air Heating Coils (H). 

When the heat pump operates, it transfers heat from the constant temperature ground source to the incoming air with a 300-400% efficiency.  If this mode is active, but the Slaby Heating mode (AH) is not, then the low thermal capacity of the Water/Air heat exchanger may cause the Heat Pump to cycle too quickly.  Possible ways to remedy this would be to a) use a Heat Pump with a low and high operating mode, b) add additional hot water storage to the Air Heating Coil circuit to boost it's thermal capacity.

AD AD is short for Air Dehumidification and is used to dehumidify incoming air, without an excessive drop in incoming air temperature. In this mode, the heat pump acts like a traditional dehumidifier.  It first cools the incoming humid air to condense out excess moisture, and then it reheats it using much of the energy removed during the cooling process.

One circuit connects the Air Cooling Coils (C) to the Heat Pump Source (Ls).  The other circuit connects the Heat Pump Delivery (Ld) to the Air Heating Coils (H). 

When the heat pump operates, it removes water vapor from the incoming air with a 300-400% efficiency.  If this mode is active, but the Slab Heating (SH) or Cooling (SC) modes are not, then the low thermal capacity of the Water/Air heat exchangers may cause the Heat Pump to cycle too quickly.  Possible ways to remedy this would be to a) use a Heat Pump with a low and high operating mode, b) add additional  water storage to the heat exchanger circuits to boost their thermal capacity.

AG AG is short for Air Ground, and is used to cool/heat the incoming air at a moderate rate.  This Passive Cooling mode is extremely efficient but  it only has a limited cooling/heating range because it's dependant on the absolute earth temperature.  Possible uses for this mode would be to dehumidify incoming air when the dew-point is very low, or simply as supplemental cooling in mild conditions.  It could also be used to pre-heat extremely cold winter air.

A single circuit is used to circulate water between the Ground Loop (K) and the Air Cooling Coils (C)

Only a fractional horsepower (300-500W) pump is required to achieve this mode.

AC AC is short for Air Cooling, and is used to rapidly cool the incoming air.  This Active Cooling mode is required when the AG mode is not capable of maintaining the desired air temperature.

One circuit connects the Air Cooling Coils (C) to the Heat Pump Source (Ls). The other circuit connects the Heat Pump Delivery (Ld) to the Ground loop (K).   

When the heat pump operates, it transfers heat from the incoming Air to the constant temperature ground sink with a 300-400% efficiency.  If this mode is active, but the Slab Cooling mode (SC) is not, then the low thermal capacity of the Water/Air heat exchanger may cause the Heat Pump to cycle too quickly.  Possible ways to remedy this would be to a) use a Heat Pump with a low and high operating mode, b) add additional cold water storage to the Air Cooling Coil circuit to boost it's thermal capacity.

In addition to the 8 pure primary and secondary modes listed above, there are also sixteen different mixed Primary/Secondary mode pairs possible with the GREEN HVAC system.  These combinations are described on the  Mixed Modes  page.

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An exercise in Energy Smart, Not So Big living.
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This site is all about building a cool, energy efficient house, that makes maximum use of earth sheltered design, passive solar heating and cooling, geothermal exchange energy management, and right sizing of the house for it's designated use. The home's placement is on a south-facing hillside in Deep Creek Lake, Maryland. This site describes the design process, the technologies used and the expected results. We also have a comprehensive Links Page for anyone who is also interested in designing a similar project.