View
218
Download
5
Category
Preview:
Citation preview
March 2010 Mumbai Delhi Chennai Kolkata
Section III : Operating Principles
Introductory Seminar on
Ground Source Heat Pump Systems
Funding support from Government of Canada gratefully acknowledged
SAP 000000-000000
Programme T002
Ground Source Heat Pump Systems
2
Section sequence
Water-based geothermal systems & heat exchanger types
Standing Column Well systems
Direct Expansion systems
Heat pumps Heat pumps
Desuperheaters
Distribution network / configuration
3
Two Types of Geothermal Heat Exchanger
OPEN LoopCLOSED Loop
Water-based geothermal
4
Inside the heat pump, a heat exchanger allows energytransfer between the heat transfer fluid (coming from the ground loop) and the refrigerant (inside the heat pump).
Water-based geothermal
5
Water-based geothermal
Heat transfer fluids may include a diluted mix of chemicals (closed loop) or groundwater (open loop) exchanging heat with refrigerant inside the heat pump.
Water is the solvent or principal component (hence the name water based).
A separate circulation pump is required to move liquid at a minimum of 2 ft per second, in commercial application.
These systems are most common but a questionable future for open loop in India and in other countries.
For open loop systems, scaling and corrosion are principal concerns, hence groundwater quality is key.
6
Open loop
Groundwater systems can be pursued only if groundwaters are sufficient in quality and in quantity, if sustainable reinjection methods exist (i.e. wells that will accomodate, in to the same aquifer) and if local regulations
Water-based geothermal
accomodate, in to the same aquifer) and if local regulations permit their installation.
Groundwater systems should use a plate heat exchanger constructed with corrosion-resistant materials (ex: stainless steel 304) between the building loop and groundwaters.
7
Open loop
Water-based geothermal
Conventional Sampling:
Weighted unit is lowered in to an open
Ground Water Sampling & Analysis
lowered in to an open borehole, line is marked with distance. Trap is opened with a separate line and unit is withdrawn.
8
Open Loop
When using a submersible pump, we install a well cap or watertight device to block the entry of surface water or other contaminant.
Proper placement of well caps and
Water-based geothermal
Proper placement of well caps and groundwater contamination are a major issue for local and state-level governments, and invite scrutiny as well as insurance questions.
9
Closed loop
Systems with underground closed loops work with polyethylene heat exchange piping in grouted vertical boreholes or horizontal trenches. The HXs are connected in series and/or in parallel, and lead to the building where theyre connected to interior (HVAC) systems.
Water-based geothermal
theyre connected to interior (HVAC) systems.
Most southern-latitude systems use water with anti-scaling and anti-corrosion agents. Most northern latitude-systems require some sort of antifreeze.
Some commercial / institutional systems use playgrounds, parks, or other public places for installation of ground loop.
10
Closed loop three common types
Water-based geothermal
Horizontal Vertical Submerged
11
Closed loop what to use?
Available ground area is a determining factor. Horizontal heat exchangers require more surface area per ton required.
Water-based geothermal
Spacing between boreholes / loops must be carefully considered this relates to thermal interference.
Differing characteristics of the site and soil will determine spacing and depth of vertical boreholes.
12
Soil characteristics can also dictate loop choices (see table C5 in Annex C to CSA C-448).
Properly sized and installed, a horizontal HX will perform just as well as a vertical heat exchanger. Operational costs will be
Closed loop what to use?
Water-based geothermal
well as a vertical heat exchanger. Operational costs will be comparable.
The choice around a classic horizontal loop or for a slinky loop, will depend on the site and the relative cost of pipe and trenching.
Horizontal fields often suffer a thermal interference penalty due to sub-optimal installation practises.
13
VERTICAL CLOSED LOOP Jobsite
Water-based geothermal
14
VERTICAL CLOSED LOOP Jobsite
Water-based geothermal
15
Can we combine the three types?
No problem. A site can utilize all three types in a single application.
Each circuit type (vertical, horizontal, slinky, DX etc) will
Water-based geothermal
Each circuit type (vertical, horizontal, slinky, DX etc) will require its own circulation pump.
This flexibility is both a blessing and curse
In the commercial sector, vertical loop dominates.
16
Standing Column Well Systems
17
Standing Column Well Systems
18
Standing Column Well Systems
Standing Column Wells (SCW) are not currently regulated or standardized in North America.
SCW systems are relatively very rare seen in New York and few applications generally.
Harvard U built a project with 15 wells in 2007 and has claimed excellent performance.
A strong resemblance exists between SCW systems and open loop groundwater systems.
SCW may be the future of most commercial projects, but is limited by geology.
19
Refrigerant circulates directly through the loop, and efficiency is thus higher than a water-based system at this level.
No circulation pump is used, i.e the system pressure comes from the
Direct Expansion Systems
system pressure comes from the compressor and heat pump itself..
Unlike a water-based GX system, a longer loop will reduce the efficiency of the system.
Adequate return flow of system oil is a critical issue in DX systems.
20
Direct Expansion Systems
Direct Expansion (DX) systems are mostly seen at the residential and small commercial level.
DX technology is in the Global Quality GeoExchange Program.Program.
In the market, no accurate software really exists to help optimize loop length. Heat pump manufacturer specifications must be followed re. loop length.
21
Contrary to the residential sector, in commercial the heat pump runs constantly (residential average ~30 min/hr).
Because of this, DX loops should be longer, as the
Direct Expansion Systems - Limits
Because of this, DX loops should be longer, as the ground has a limited heat storage capacity per unit volume.
As above, DX system efficiency is mostly related to optimum loop length. Beyond or before this optimum length, the system loses efficiency.
22
The heat pump
A heat pumps mechanical principle in cooling is essentially the same as a refrigerator.
In heating mode, the cycle is inverted.
Geothermal heat pumps in North America use very low Geothermal heat pumps in North America use very low grade (i.e. cold temperature) heat to heat buildings. Mechanical work is required to extract and make the heat usable; heat pumps are excellent for this.
In India, extreme cooling needs in warm temperatures mean that Canada is the most appropriate comparison - it is the inverse extreme.
23
The heat pump
24
DesuperheaterA desuperheater is a refrigerant
water heat exchanger situatedbetween the compressor and the condenser.
A pump circulates cold water fromthe bottom of the reservoir towardthe desuperheater, where the superheated gas from the refrigerant heats it. The heatedrefrigerant heats it. The heatedwater is reinjected at the top of the reservoir.
Q: Why does this component runat a much higher efficiency whenthe system is in cooling mode?
The heat transferred fromdesuperheaters is on the order of 1.5 kW for a 3 ton.
Commercial systems usually preheatdirectly from a boiler due to efficiencies and volumes of available heat vs requirements
25
Heat pumps may distribute output in two ways:
- air
- water
Heat may be distributed through conventional
Distribution networks & methods
Heat may be distributed through conventional systems air ducting, water lines
Why is hydronic an especially good fit for geoexchange technology?
26
Distribution networks & methods
HYDRONIC (water) Commercial office buildings with high loads / demands, and multiple zones, are ideal for hydronic distribution.distribution.
27
Distribution networks & methods
HYDRONIC (Water)
A heat pump can provide cold water for:
Zoned in-floor cooling (caution: humidity);
A fan coil for pulse air systems;
Industrial cooling (ice rinks, refrigeration); Industrial cooling (ice rinks, refrigeration);
Refrigeration, and other purposes.
A heat pump can provide hot water for:
Zoned heating systems, automated or dumb;
Domestic hot water and industrial needs;
Pool or spa heating;
A fan coil for pulse air systems, snowmelt, other purposes.
28
HYDRONIC (water)
A fan coil system with 4 pipes designed for water at 45F (7C) and heated water at 110F (43C) heats and cools the entire building.
Distribution networks & methods
building.
Three-way valves allow both heated and chilled water to circulate within internal HX coils when heat / cool is not needed.
29
HVAC System Issues - Air
Better envelope / insulation will help all systems perform more efficiently, and so will optimizing the distribution system choice.
Ducts must be sized for geothermal systems often
Distribution networks & methods
Ducts must be sized for geothermal systems often larger sized for larger volumes at less extreme temps / slower speeds.
Acoustic isolation must be installed both on the air intake / feeder side and the output side; in the first four feet (1.22 m) or horizontal ducting.
Air return ducts must have large-radius turns.
30
Distribution networks & methods
HVAC system Equipment type
Vertical equipment
Return air usually comes from the mechanical room. Note the filters at the point of air entry.
Horizontal equipment (suspended from ceiling)
Return air is usually carried through conduits.
31
Distribution networks & methods
Some Key Design Issues
1) Learn and remember the temperature range that the equipment is designed to use / output.
2) Choose the BIN data to match system size and meet client price expectations (use software).
3) Design the system so that the flow is appropriate to 3) Design the system so that the flow is appropriate to the interior both of the evaporator and the condensor.
4) Choose a distribution system to maximise overall system performance.
5) Optimize the overall system to maximise simultaneous heating cooling possibilities.
6) Research other potential heat sources or sinks, to take best advantage of heat pump technology strengths.
32
Terminology
See any CGC course for a full glossary.
Major terms:
Standing Column Wells
DX Direct Expansion DX Direct Expansion
Desuperheater
Hydronic distribution
Thermal storage
33
QUESTIONS OR COMMENTS ?
Above: Fifth Town Artisan Cheese Factory Winner, 2007 CGC
Central Canada Prize for Project Excellence
Burnaby BC Seniors Home
Recommended