A water-cooled chiller removes heat from a chilled-water or water-glycol loop, then rejects that heat through a separate condenser-water loop, usually with a cooling tower. The right unit is the one that meets the real load at full and part load, fits the available water quality and footprint, and comes with rating, controls, heat-exchanger, and commissioning evidence that an engineer can check. This guide turns those decisions into a usable RFQ without treating a nameplate tonnage as a complete design.
What a water-cooled chiller actually does
Inside the chiller, refrigerant absorbs heat in the evaporator, is compressed, and rejects heat in the condenser. The chilled-water loop carries useful cooling to air handlers, process heat exchangers, or other terminal equipment. The condenser-water loop carries rejected heat to a cooling tower or another heat-rejection device. The loops exchange heat through metal surfaces; the process water and refrigerant do not mix.
ASHRAE chilled-water plant overview treats the chiller as one part of a plant that also includes pumps, piping, controls, heat exchangers, and commissioning. That systems view matters when a replacement chiller seems to fit the available footprint but its flow, pressure drop, or control sequence does not match the rest of the plant.
The phrase “water-cooled chiller” describes the heat-rejection method, not a single compressor technology or a guaranteed efficiency level. A screw chiller, centrifugal chiller, or compact scroll package can all use condenser water. Specify the duty and constraints first, then compare package types on the same rating basis.
Record the design point before comparing models
Start with the load profile rather than a preferred brand or nominal tonnage. A facility may have a high afternoon peak but spend most hours at 40% to 70% load. A process may need a tight leaving-water temperature even when the total load is modest. Both cases change the sensible choice of compressor, number of machines, controls, and heat-exchanger surface.
Use the following fields as a minimum data sheet. Values described as examples are screening points, not universal setpoints.
| Input to record | Why it changes selection | Доказательства для запроса | Распространенная ошибка |
|---|---|---|---|
| Peak and hourly cooling load | Sets capacity, staging, and turndown requirement | Load calculation or measured trend with units and duration | Selecting from peak tons only |
| Chilled-water supply and return | Sets evaporator temperature difference and flow | Design temperatures, allowable reset range, glycol percentage | Quoting a leaving temperature without return temperature |
| Condenser-water supply and return | Sets condensing pressure, tower duty, and tube velocity | Entering water temperature, flow, fouling allowance, winter limit | Using outdoor dry bulb instead of the condenser-water condition |
| Flow, pressure drop, and connection geometry | Determines pump head, nozzle size, and installation fit | GPM or L/s, allowable pressure drop, flange standard, service clearances | Treating pipe size as proof of required flow |
EPA WaterSense chilled-water guide illustrates a chilled-water supply around 38°F to 45°F with a 10°F to 20°F rise, and condenser water around 80°F to 85°F with a 10°F to 20°F rise. Those ranges help a buyer ask complete questions, but the project design, fluid, climate, and terminal equipment must set the final values.
Wet bulb, approach, and seasonality
Water-cooled equipment can benefit from a condenser-water temperature tied to outdoor wet-bulb conditions, especially when a cooling tower is available. The approach between tower leaving water and outdoor wet bulb, tower fan turndown, and winter freeze strategy all influence the condenser entering condition. Ask for performance at the design summer point and at the lowest controlled condenser-water temperature rather than one catalog row.
If the plant operates in a dry climate or faces water restrictions, compare the water and energy budgets together. A water-cooled chiller may reduce compressor power at favorable wet-bulb conditions, but it adds pumps, tower fans, treatment, blowdown, makeup water, and freeze protection. An air-cooled alternative may have a simpler installation even when its full-load efficiency is lower. The decision is a life-cycle comparison, not a universal ranking.
Match compressor technology to load and service reality
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| cURL Too many subrequests by single Worker invocation. To configure this limit, refer to https://developers.cloudflare.com/workers/wrangler/configuration/#limits | Действия покупателя | Ответ поставщика на запрос | Проверка выпуска |
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| 2. Screen architecture | Compare one machine, N+1, or parallel modules | Plant sequence, minimum load, and standby behavior | The common load band is inside the useful turndown range |
| 3. Check water side | Provide chemistry, fouling factor, pressure drop, and connection data | Tube materials, velocity, pressure rating, and cleaning method | Nozzle, flange, pump, and service clearances fit |
| 4. Validate economics | Add pumps, tower, treatment, controls, electricity, and water | Full-load and part-load data on a common rating basis | Life-cycle assumptions are documented, not implied |
Oversizing can leave a machine cycling or operating away from its efficient range. Undersizing can force a second machine to run continuously or leave the process without a recovery margin. If the load profile is uncertain, request a sensitivity selection for the design load, the typical load, and the future expansion case.
Check efficiency, controls, and water management together
U.S. Department of Energy FEMP chiller guidance separates full-load and integrated part-load requirements and points buyers to AHRI 550/590 test procedures. Ask for both values, the test conditions, and the expected plant kW per ton at the load bands that matter. A single peak rating cannot predict annual energy use.
Controls should coordinate the chiller, condenser-water pumps, tower fans, chilled-water pumps, bypasses, and terminal valves. Verify sensor locations, reset limits, minimum flow, staging delays, alarm outputs, and the sequence used when a machine is isolated. If the plant uses variable-speed drives, request the control points and trend list that will prove the sequence after handover.
Treat condenser water as a design boundary
Condenser water is a design boundary, not a utility connection alone. Suspended solids, hardness, chlorides, biological growth, and concentration cycles affect tubes and tower equipment. The AHRI liquid-chiller guidance describes treatment, blowdown, and condenser-tube cleaning as part of water-cooled operation. Put the treatment limits, sampling frequency, filtration, chemical responsibility, and cleaning access in the RFQ.
The plant owner should also document who owns Legionella risk management, tower cleaning, chemical storage, and discharge compliance. A closed chilled-water loop does not remove the treatment responsibility from an open condenser-water loop. Conversely, a well-controlled water loop can protect the chiller and reduce avoidable energy loss from scale.
Require commissioning evidence beyond a start-up statement
Commissioning should show that the installed chiller meets the design intent under safe, repeatable conditions. The ASHRAE plant-design course outline includes functional testing, point-to-point checks, trend reviews, and procurement evidence for a reason: the chiller, pumps, valves, sensors, and terminal equipment behave as one system.
Request a signed record that identifies the instruments, calibration status, test conditions, and measured values. Keep the results for the design load and at least one representative part-load condition. If the test cannot reach design conditions on the day, record the limitation and define a repeat test rather than marking the package complete.
| Evidence item | What it should show | Зачем это нужно отделу закупок |
|---|---|---|
| Factory rating and selection sheet | Capacity, power, temperatures, flow, refrigerant, and rating basis | Makes bids comparable and exposes hidden assumptions |
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Часто задаваемые вопросы
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A water-cooled chiller uses refrigerant to remove heat from a chilled-water or water-glycol loop. The refrigerant rejects that heat through a condenser to a separate condenser-water loop, which normally carries it to a cooling tower. Pumps, valves, controls, and heat exchangers are part of the plant selection even though they are outside the chiller shell.
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An air-cooled chiller rejects heat directly to outdoor air through fans. A water-cooled chiller rejects heat to condenser water and normally needs a tower, pumps, treatment, and freeze protection. Water cooling can support large capacities and lower condensing temperatures, while air cooling usually simplifies installation and avoids tower water management.
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For water near standard properties, estimate Btu/h as 500 multiplied by GPM and the water temperature difference in °F. Divide by 12,000 for approximate tons. Confirm the result with the actual fluid, load profile, design temperatures, pressure drop, standby requirement, and a supplier selection at the rating conditions.
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Request full-load and integrated part-load values on a common rating basis, plus entering and leaving water temperatures, flow, fouling assumptions, electrical input, and the control sequence used in the calculation. AHRI 550/590 and current project or procurement requirements should define the rating method. Do not compare a single peak number from different conditions.
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State the condenser-water chemistry limits, filtration, treatment and blowdown responsibility, sampling schedule, biological-control plan, tube-cleaning method, and discharge constraints. Also state the chilled-loop fluid and glycol concentration. The chiller, tower, and treatment vendor must agree on the boundary so that scale and corrosion allowances are not left ambiguous.
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