Deep Lake Water Cooling Feasibility Calculator
This calculator helps you estimate whether deep lake water cooling (DLWC) can offset or replace mechanical chillers for a given building. By combining your cooling load, lake and building temperatures, pumping requirements, and energy costs, it approximates energy savings, operating cost savings, emissions reductions, and simple payback for a deep lake system.
Use it as a preliminary screening tool during concept design or decarbonization planning. It does not replace detailed engineering analysis, hydraulic modeling, or regulatory review.
How deep lake water cooling works
Deep lake water cooling relies on the naturally low temperature of water at depth in large lakes. Instead of using mechanical chillers to remove heat from the building, cold lake water absorbs this heat through heat exchangers and is then returned to the lake or a discharge location. Mechanical chillers may still be required for peak loads or to trim supply temperatures, but their runtime and energy use can be greatly reduced.
The key questions this calculator helps you answer are:
- Is the temperature difference between lake water and building return large enough to provide useful cooling?
- How much pumping power is needed to move water between the lake and the building?
- How do pumping energy needs compare to the energy a conventional chiller would use?
- Do the expected energy and emissions savings justify the capital cost?
Key formulas used in the calculator
At a high level, the calculator compares the annual electrical energy use of a baseline mechanical chiller to the pumping energy required for deep lake cooling. It then converts the difference into cost and emissions savings and estimates simple payback from the capital cost you enter.
1. Cooling load and chiller energy
The design cooling load you enter is in refrigeration tons (1 ton of cooling = 3.517 kW of heat removal). The calculator converts this to kW and uses your baseline chiller COP (coefficient of performance) to estimate the electrical input required.
Cooling capacity in kW:
Baseline chiller power in kW:
Chiller kW = Q / COP
Annual chiller energy use in kWh:
Chiller kWh/year = Chiller kW × Annual operating hours
2. Cooling potential from deep lake water
The available temperature difference between the building return water and the lake supply water determines how much heat can be transferred per unit of flow through a heat exchanger. In practice, limits such as minimum approach temperature, fouling, and flow constraints apply. This calculator assumes the design load you enter is achievable with the deep lake supply temperature you provide, and it focuses on the energy comparison rather than detailed thermal sizing.
3. Pumping power estimate
Pumping power depends on flow rate, total dynamic head, and pump efficiency. In this simplified screening tool, the detailed flow calculation is internal, but the fundamental relationship is based on hydraulic power:
where:
- Ppump is the pump power (W)
- ρ is water density (kg/m³)
- g is gravitational acceleration (m/s²)
- Q is volume flow rate (m³/s)
- H is total pumping head (m)
- η is pump efficiency (decimal)
You provide the total pumping head and pump efficiency. The tool infers an approximate flow from your cooling load and temperature difference and then estimates pump power and annual pump energy.
4. Cost, emissions, and payback
With annual energy use for both cases, the calculator determines:
-
Annual operating cost for each option:
Cost = kWh/year × Electricity price -
Annual emissions for each option:
Emissions = kWh/year × Grid emissions factor -
Annual savings compared to the baseline chiller:
Energy savings = Chiller kWh − Pump kWh
Cost savings = Chiller cost − Pump cost
Emissions reduction = Chiller emissions − Pump emissions
Simple payback (years) is then approximated as:
Payback = Deep lake system capital cost ÷ Annual cost savings
How to interpret the results
When you run the calculation, you will typically see estimates for:
- Annual energy use for the baseline chiller and the deep lake system
- Annual operating cost for both cases
- Annual greenhouse gas emissions for both cases
- Energy, cost, and emissions savings
- Simple payback period based on the capital cost you entered
A deep lake option is usually more attractive when:
- The lake supply temperature is consistently low (for example, below 8–10 °C).
- The building return temperature is relatively high, giving a good temperature difference for heat transfer.
- Annual operating hours are high (e.g., district cooling, data centers, or large commercial loads).
- Total pumping head is modest and pump efficiency is good.
- Electricity prices and grid emissions factors are high, making energy savings more valuable.
A short payback period (for example, under 10 years) and significant annual emissions reductions indicate a strong candidate for deeper feasibility study. A long payback or small savings may suggest that conventional high-efficiency chillers or other efficiency measures remain more cost effective.
Worked example
Consider a large office or institutional building with the following inputs:
- Design cooling load: 2,000 tons
- Lake supply temperature: 6 °C
- Building return temperature: 12 °C
- Annual operating hours: 3,000 hours
- Total pumping head: 40 m
- Pump efficiency: 80 %
- Electricity price: $0.12/kWh
- Baseline chiller COP: 5.5
- Deep lake system capital cost: $25,000,000
- Grid emissions factor: 0.35 kg CO₂e/kWh
The calculator will convert 2,000 tons to about 7,034 kW of cooling. With a COP of 5.5, the baseline chiller would draw roughly 1,280 kW at full load. Over 3,000 hours, this is on the order of 3.8 GWh/year of electricity.
Based on the temperature difference and your pumping head and efficiency, the calculator estimates the flow and pump power needed to deliver a similar amount of cooling with deep lake water. If, for example, the modeled pump power is around 500 kW, the annual pump energy might be about 1.5 GWh/year.
In this illustrative case, annual savings compared to the chiller could be roughly:
- Energy savings: ~2.3 GWh/year
- Cost savings: ~2.3 GWh × $0.12/kWh ≈ $276,000/year
- Emissions reduction: 2.3 GWh × 0.35 kg/kWh ≈ 805 t CO₂e/year
A capital cost of $25 million divided by $276,000/year yields a simple payback of about 90 years in this hypothetical case. That would generally be unattractive, highlighting that either capital cost must be lower, hours higher, or electrical and emissions savings greater for the project to be compelling. You can experiment with different loads, hours, electricity prices, and capital costs to see how sensitive payback is to each factor.
Deep lake vs. mechanical chiller: high-level comparison
The table below summarizes some typical contrasts between a deep lake water cooling system and a conventional mechanical chiller plant. These are generalized tendencies based on screening-level assumptions; actual project outcomes will vary.
| Aspect | Deep lake water cooling | Mechanical chiller plant |
|---|---|---|
| Primary energy driver | Pumping power to move lake water and building water | Compressor power in electric chillers |
| Typical operating energy use | Lower, especially for large, steady loads and cold lakes | Higher, scales directly with cooling load and COP |
| Emissions impact | Can significantly reduce emissions where the grid is carbon intensive | Emissions proportional to chiller electricity use |
| Capital cost | Often high, including intake, piping, and heat exchangers | Lower for standalone building systems; may still be substantial for large plants |
| Site and permitting constraints | Requires access to a deep, cold lake and regulatory approval | Fewer site constraints, but may need cooling towers and makeup water |
| Resilience and redundancy | High resilience if combined with backup chillers and robust intake design | Well-understood technology; redundancy achieved with multiple chillers |
| Best fit applications | District cooling, campuses, data centers, dense urban cores near deep lakes | Most individual buildings and sites lacking access to deep water |
Assumptions and limitations
This is a simplified feasibility screening tool. It is intended to provide a quick, order-of-magnitude indication of whether deep lake water cooling may be technically and economically attractive. Key assumptions and limitations include:
- The lake supply temperature you enter is achievable and stable during the operating season.
- Heat exchanger performance, fouling factors, and approach temperatures are represented only implicitly.
- Pumping head is provided as a single value and does not differentiate between static lift, friction losses, or minor losses.
- Pump efficiency is treated as constant across the operating range.
- Cooling load and operating hours are assumed to be steady or average values; load variation over time is not modeled.
- Grid electricity price and emissions factor are assumed constant over the year.
- Capital cost is treated as a single upfront amount and financing, tax effects, and residual value are not modeled.
- Environmental and regulatory aspects such as lake thermal impacts, intake design, and discharge permitting are outside the scope and must be evaluated separately.
Use the outputs to prioritize where more detailed engineering and economic studies are warranted, rather than as a final basis for investment or permitting decisions.
Why Deep Lake Cooling Matters
Deep lakes and reservoirs stay cold year-round, even as surface temperatures swing wildly. Cities like Toronto, Stockholm, and Ithaca have tapped that stratified cold water to provide district cooling without the energy intensity of mechanical chillers. Drawing water from 50 meters or more below the surface gives engineers a stable supply around 4 °C. Passing that water through heat exchangers can absorb building heat and dump it back into the lake at slightly warmer temperatures while the remaining water is discharged at depth. The approach slashes electricity consumption, frees grid capacity for electrification, and cuts refrigerant leakage risk. Yet many communities lack a quick way to test feasibility when a mayor or developer asks, “Could our lake do this?” The Deep Lake Water Cooling Feasibility Calculator provides that first-cut assessment. By entering the cooling load, lake temperatures, pumping head, and cost assumptions, you can see how much energy would be saved relative to a chiller plant and what the payback might look like.
As with all AgentCalc tools, the page is a single HTML file with inline JavaScript and no external dependencies. It respects the house styling defined in _main.css, ensuring the interface matches the other calculators your team already trusts. Every input is validated so that you never run a scenario with negative flow, zero temperature difference, or impossible pump efficiency. The result block uses friendly language to describe when a plan fails—for example, if the required temperature drop is non-positive—so you can correct the data before presenting results to stakeholders.
Core Formulas
Deep lake cooling trades compressor work for pumping energy. The thermal load you enter in refrigeration tons is converted into kilowatts and then divided by the product of water’s specific heat and the temperature rise you allow in the return stream to find volumetric flow. Pump power depends on that flow, the elevation change, and efficiency. The mechanical chiller baseline power is simply the load divided by the chiller COP. The MathML equation below captures the pumping power relationship:
In this relationship, is water density (1,000 kg/m³), is pump efficiency, is gravitational acceleration (9.81 m/s²), is volumetric flow in cubic meters per second, and is the total head in meters. The calculator multiplies the result by 1,000 to convert kilowatts to watts when needed, ensuring consistent units. Annual energy savings are the difference between the chiller and pumping electricity over the operating hours you specify. Those savings drive the economic and emissions outputs.
Worked Example
Suppose a university campus requires 18,000 tons of cooling at peak and expects to run the plant 3,500 hours per year. A nearby lake delivers 4.5 °C water at 75 meters depth, and the building loop can return water at 12 °C, yielding a 7.5 °C temperature differential. Engineers estimate 60 meters of total dynamic head when accounting for intake risers and distribution friction, and high-efficiency pumps with 82 percent combined efficiency are available. The campus currently operates chillers with an average COP of 5.3. Electricity costs $0.09 per kWh and the grid emits 0.14 kg CO₂e per kWh. Building intake pipes, filtration, and plate heat exchangers are projected to cost $140 million. Plugging those numbers into the form yields a thermal load of 63,306 kW. The required flow is 2.01 cubic meters per second. Pumping power lands near 1,439 kW, whereas the chiller baseline draws almost 11,945 kW. Over the year, the deep lake system would consume 5.0 GWh versus 41.8 GWh for chillers, saving 36.8 GWh annually. That equates to $3.3 million in avoided electricity costs and 5,152 metric tons of CO₂e avoided. The simple payback on $140 million is long—about 42.7 years—but grants, resilience benefits, and the ability to expand service to new buildings can improve the business case.
Scenario Comparison
The table below illustrates how temperature differential, pump efficiency, and operating hours influence payback. Use it as a template when exploring other lakes or when bundling deep water cooling with demand management strategies explored in the building pre-cooling energy savings calculator.
| Scenario | Temperature Rise (°C) | Annual Energy Savings | Electricity Savings | Simple Payback |
|---|---|---|---|---|
| Base case | 7.5 | 36.8 GWh | $3.3 million | 42.7 years |
| Improved pump efficiency | 7.5 | 37.6 GWh | $3.4 million | 40.8 years |
| Higher return temperature | 9.0 | 41.9 GWh | $3.8 million | 36.6 years |
Raising the allowable return temperature widens the thermal lift, reducing the required flow and the associated pumping energy. Alternatively, investing in premium pump sets has a modest but meaningful impact on savings. Decision makers often cross-reference these scenarios with the district energy decarbonization phasing calculator to determine how deep lake cooling slots into a long-term energy roadmap. Pairing the analysis with the pumped hydro storage sizing calculator also helps illustrate how lake infrastructure might support other grid services.
Limitations and Assumptions
This calculator assumes that the lake water is abundant, clean, and accessible year-round. It does not model thermal plumes or ecological impacts, which require detailed limnology studies and regulatory approval. Intake filtration, zebra mussel control, and seasonal stratification management introduce operational costs not captured here. We treat the lake water and building loop as separate, assuming a closed-loop heat exchanger to avoid contamination. Pumping head is assumed constant even though friction losses can vary with flow; the sensitivity analysis should therefore include conservative head estimates. The financial metrics exclude maintenance savings from retiring chillers or avoiding refrigerant purchases. Simple payback ignores the time value of money; use the output as a screening tool before developing a full net-present-value model.
Implementation Roadmap
If the calculator suggests a promising opportunity, the next steps include bathymetric surveys, environmental permitting, and detailed hydraulic modeling. Teams often install a pilot-scale intake to verify temperature stability across seasons. Because the deep lake system still requires auxiliary chillers for redundancy, compare hybrid operations using the HVAC cooling load calculator to ensure transition plans keep buildings comfortable. Engage local utilities early; they may offer incentives similar to those captured in the community resilience hub microgrid sizing calculator. Finally, communicate co-benefits—such as freed electrical capacity for electrified heating or electric vehicle charging—to secure stakeholder buy-in. With rigorous validation and transparent assumptions, this calculator equips you to lead that conversation.