section iii : operating principles oa... · • groundwater systems should use a plate heat...

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

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Section sequence

Water-based geothermal systems & heat exchanger types

Standing Column Well systems

Direct Expansion systems

Heat pumps Heat pumps

Desuperheaters

Distribution network / configuration

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Two Types of Geothermal Heat Exchanger

OPEN LoopCLOSED Loop

Water-based geothermal

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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).


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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.

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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


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.

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Open loop


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 Trap is opened with a separate line and unit is withdrawn.

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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


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.

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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.


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.

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Closed loop three common types


Horizontal Vertical Submerged

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Closed loop what to use?

Available ground area is a determining factor. Horizontal heat exchangers require more surface area per ton required.


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.

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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?


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.

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VERTICAL CLOSED LOOP Jobsite


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VERTICAL CLOSED LOOP Jobsite


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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


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.

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Standing Column Well Systems

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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.

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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.

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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.

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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.

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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.

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The heat pump

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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

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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?

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HYDRONIC (water) Commercial office buildings with high loads / demands, and multiple zones, are ideal for hydronic distribution.distribution.

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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.

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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.


building.

Three-way valves allow both heated and chilled water to circulate within internal HX coils when heat / cool is not needed.

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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


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.

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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.

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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.

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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

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QUESTIONS OR COMMENTS ?

Above: Fifth Town Artisan Cheese Factory Winner, 2007 CGC

Central Canada Prize for Project Excellence

Burnaby BC Seniors Home

section iii : operating principles oa... · • groundwater systems should use a plate heat...

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