Ground heat exchanger GHE
The ground heat exchanger is well-known component of the ventilation system and recuperation . It involves placing deep underground (minimum 1.5m) in the form of heat exchanger tubes of large cross-section (eg 200mm ) or deposits of gravel .
The idea of working the ground heat exchanger is to use the energy of the earth for cooling air for mechanical ventilation in summer ( a few degrees ), and heating it in winter with a similar value . Clean air going through the ground heat exchanger uses the energy of the ground by reducing expenditures on additional heating and cooling of the air , despite the assurance of forced mechanical ventilation providing fresh air from the outside .
This air is heated (in winter ), in two or more steps before blowing the premises :
- passage through the ground heat exchanger causes its temperature rises by up to several degrees , with high frost (-20C) rarely falls below 0C GHE output and almost does not depend on the outside temperature .
- preliminary , additional heating of the air by water wells or solar panels for another few to several degrees before entering the recuperator
- heating through the heat recuperator . Recuperator heat exchanger can be of any type (cross , rotation , opposed ) . It works on the principle of heating the clean and cold supply air from the outside through dirty and warm exhaust air out of the house .
- air heating to the required value electric heater or water heater before serving home air . Depending on the type of recuperator, heat is output from the Automatic , which warms the air clean to the setpoint temperature – blown to the premises .
- Additional external water heater for leaving the recuperator – using a heating vent ( blow )
Taking into account the installation of ground heat exchanger once we decide on mechanical ventilation or recuperation . Type GHE should also think about taking into consideration not only the cost but also the characteristics of each .
requires burying the long ( over 50 m ) of the tube to a depth of at least 1.5 meter . The pipe must be laid with a fall in order to ensure the possibility of condensation of dew to one place ( manhole air intake ) . This water must be periodically selected manually or automatically . To perform such a heat exchanger , in some cases it is necessary to perform very large earthmoving backhoe digging up a significant part of the plot .
For houses with basements may consider laying pipes around the foundation basement ( at least one meter away from him) which significantly reduce excavation and digging a large part of the plot . Please note that the land unless thickened will settle very slowly and unevenly , leaving a trace for years .
Some manufacturers of ground heat exchanger pipe sell ready-pipe systems with approval anti fungal , sanitation , etc. . In addition, apparently have better heat transfer characteristics between the air and the surface of the pipe . However, they are much more expensive than standard sewer pipes of the same diameter , which results in very frequent use of alternatives .
In the case of tubular heat exchanger must also be taken into account that , it is not possible to clean or wash several dozen tube in one piece , located a few meters under the ground . In this context, it is difficult to determine what happened to her will happen and how it will look in a few or several years . It is also difficult to determine whether it will become a habitat for fungi , mold , diseases and allergies in the future .
The efficiency of ground heat exchanger of this type depends primarily on the depth of the pipe , its length, , soil type and groundwater level .
Ground Heat Exchanger and gravel filter
Another option ground heat exchanger is the so-called gravel filter . Depends on the fact that we deep down in the earth large sealing and isolating it from the ground foil native . Down the gravel backfill ( volume to 10m3 ) passing through the air before entering the recuperator . To perform this method GHE , required is low groundwater levels throughout the year , far below the bottom of the GHE . Gravel filters also equipped with sprinklers to allow periodic flushing of gravel deposits . This filter requires no digging the whole plot and can be installed on a much smaller area . The problem with gravel filters is the need for its regeneration (work on half-time) . This comprises two identical filters, and the switching operation every few hours .
As in the case of tubular heat exchangers is possible to produce fungal , mold , lichens and allergens in beds of gravel .
In the case of gravel filters theoretically possible exchange deposits of gravel , However, this operation is very expensive and rather unprofitable in houses . Such solutions are practiced in hospitals , where there are additional requirements of sanitary and these filters have a special design to enable and simplify the exchange of gravel deck .
Advantages and disadvantages of ground heat exchangers :
- recovery of free energy in the winter (heating) and summer (cooling)
- high cost of installation
- large amount of earthworks
- virtually no possibility of cleaning or maintenance
- possibility of fungal growth , mold , allergens in the environment GWC
- the need to use automation GWC management to achieve effective and appear to work by control dampers , assistive devices ,
control of boiler and central heating system integrated ecological
- pressure drop recuperator prevent normal operation since it produces a negative pressure in the house ( effective exhaust is stronger than supply) . Losses resulting need for booster fans GHE and additional electricity consumption .
To effectively use GHE is necessary to optimally control the operation of the GHE heating and ventilation control element of the system eHouse – Smart Home , intelligent Building and home automation .
An alternative to GHE on some plots , may well be cooling in summer and warming in winter .