Geothermal (ground-source heat pump, GSHP) cooling uses the earth’s stable temperature 1.5-3 m below grade as a heat sink for cooling. In Indian climates, with ground temperature around 22-26 °C year-round (vs surface air 35-45 °C summer), geothermal cooling can replace cooling tower + condenser water with significantly higher chiller COP.
This guide covers GSHP economics, the Indian climate fit, and where it’s actually viable.
How GSHP works
A GSHP system has three loops:
1. Building loop — chilled water to AHUs (same as conventional)
2. Refrigeration loop — heat pump transferring heat between chilled water + ground loop
3. Ground loop — water/glycol circulating through buried plastic loops in the earth
The ground loop replaces the cooling tower + condenser water loop. Heat absorbed from chilled water transfers to ground via vertical or horizontal loops.
Two ground loop types
Vertical (boreholes)
- Boreholes 50-150 m deep with U-tubes
- Footprint: small (typically 10-20 m² per borehole, 1 borehole per 7-10 kW cooling)
- Capex: ₹25-50 lakh per 100 TR (drilling-dominated)
Horizontal (trenches)
- Trenches 1.5-3 m deep with serpentine loops
- Footprint: large (typically 50-100 m² per kW cooling)
- Capex: ₹15-30 lakh per 100 TR (less expensive than vertical)
Where GSHP works in India
Suitable conditions
- Ground temperature 22-26 °C (most of India qualifies)
- Site has space for boreholes (vertical) or trenches (horizontal)
- Cooling load > 100 TR (economy of scale matters)
- Owner pursues sustainability rating (IGBC v3 EE points)
Suitable climates
- Bangalore, Pune, Hyderabad — moderate cooling, year-round demand
- Delhi NCR — high cooling, suitable for vertical
- Mumbai, Chennai — moderate suitability (high cooling load, but coastal soils variable)
Unsuitable conditions
- Very high cooling load (> 1,000 TR) — boreholes count too high
- Compact urban site without yard space
- Extremely hot soil (rare in India, but found in arid Rajasthan)
- Saturated clay soils (high resistivity, poor heat transfer)
- Low-budget projects (capex 2-3× conventional)
Economic comparison
For 200 TR cooling load over 15-year life:
| System | Capex | Annual energy | 15-yr LCC |
|---|---|---|---|
| Conventional water-cooled chiller + tower | ₹50 lakh | ₹15 lakh | ₹275 lakh |
| Air-cooled chiller (no tower) | ₹35 lakh | ₹20 lakh | ₹335 lakh |
| GSHP (vertical, 200 boreholes) | ₹100 lakh | ₹10 lakh | ₹250 lakh |
GSHP wins on 15-year LCC for moderate-cooling loads. Capex 2× conventional but operating cost 30-40% lower due to higher chiller COP (5-6 vs 3.5-4 for air-cooled).
Sizing example: 100 TR Bangalore office
Cooling: 100 TR × 60% load factor = 60 TR average.
Heat rejected to ground: 100 TR × 1.15 = ~404 kW heat.
Vertical loop: 100 m boreholes at 2 kW heat rejection each = 200 boreholes (8 m grid spacing).
Site footprint: 8 × 8 m × 200 = ~1.3 hectares (massive — only viable for campuses with land).
Alternative — Horizontal: 70 m² per kW × 404 kW = 2.8 hectares trenches. Still significant.
Where GSHP doesn’t make sense
- Multi-storey commercial in compact urban site (no roof/yard space)
- Cooling-only buildings (no heating recovery to capture)
- Indian climate above 30°C ground temperature (rare)
- Sites with rock or saturated clay geology
Hybrid approach
Many Indian projects use hybrid:
- GSHP handles 50-70% of base load
- Conventional chiller + tower handles peak
This reduces ground loop size by 30-50% while capturing most operating savings. Typical for 500-1,000 TR commercial.
Common GSHP design mistakes
1. No site geology survey. Soil thermal resistivity unknown; borehole count + spacing wrong.
2. Underestimating drilling cost. Indian drilling rates vary 5× by region; budget significantly.
3. No water-table consideration. Boreholes intercepting groundwater can short-circuit thermal exchange.
4. No corrosion protection. Glycol-water loop with mild steel = corrosion within 5 years.
5. No commissioning of ground loop. Pressure test + flow balancing required.
Quick checklist
- [ ] Site geology survey (soil thermal resistivity, water table, depth)
- [ ] Cooling load + ground rejection sizing
- [ ] Vertical vs horizontal vs hybrid decision
- [ ] Borehole count + spacing per IGSHPA guidelines
- [ ] Land/footprint requirement vs available
- [ ] Capex + LCC analysis vs conventional
- [ ] Drilling contractor selection (specialized + insured)
- [ ] Ground loop pressure test + commissioning
- [ ] Glycol-water + corrosion protection
References: ASHRAE Handbook HVAC Apps 2023 Ch 35 (Geothermal Energy); IGSHPA Closed-Loop GSHP Design Guide; IS 14681 (Geothermal energy guidelines); Indian Bureau of Mines geological maps.
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