7 Design Guides for Engineers: Absorption, Towers, Chillers, Controls

This is a series of seven "Design and Piping" guides, 614 pages in total, that we at Cold Energy (NCT) wrote for design engineers. Each guide is for an engineer who has to issue a design section tomorrow with a specific machine and has little or no experience with it: an absorption chiller, a cooling tower, a chiller, an absorption heat pump, a dry cooler, a pump station or a control panel. The level is engineering: input data, worked calculations, schematics, piping, winter operation, controls, Russian codes, typical mistakes and a final design review checklist. All seven PDFs are free to download with no registration. The PDFs are in Russian; what each one covers is summarised below in English.

What is inside each guide?

APM001. Thermax absorption chillers (50 pp.). Steam, hot water, direct-fired gas and gas-engine exhaust machines: when an absorption chiller makes sense and when it does not, choosing the machine type, the data sheet, calculations for the heat source, cooling tower, pumps, gas and flue. Separate chapters cover piping for steam, hot-water, gas-fired and exhaust-fired machines, plant room layout, start-up and shutdown, and a design review checklist.

APM002. NCT cooling towers (126 pp.). Open and closed-circuit towers: which type and series you need, input data, water balance, circuit hydraulics, tank sizing. Four circuit schematics, from a pump drawing from the tower basin to several towers in parallel on common headers, plus piping, winter modes, siting, controls, water quality and acceptance testing of tower capacity.

APM003. NCT chillers (118 pp.). Air-cooled packaged units, units for a remote condenser and water-cooled machines: selection, glycol corrections, loop pressure drop, system volume and buffer tank sizing. Chilled-water schematics (constant flow, primary-secondary, hydraulic separator, variable primary flow), evaporator and condenser piping, free cooling and adiabatic cooling, refrigerant lines, winter operation and controls.

APM004. Thermax absorption heat pumps (70 pp.). How to turn waste heat into useful heat: type 1 heat pumps and type 2 heat transformers, plus machines that deliver both cooling and heating. When an absorption heat pump makes sense, input data for every circuit, heat balance and annual benefit, heat source requirements, connection schemes and cascades, and how to check a specification you have been sent.

APM005. NCT dry coolers, air coolers and evaporative condensers (83 pp.). Dry, adiabatic and evaporative cooling: a decision tree for the unit type, surface sizing and glycol correction, spray water balance, a dry cooler on a chiller condenser, three free-cooling schemes, piping, winter operation, siting and controls.

APM006. NCT pump stations, tanks, water treatment and glycol (85 pp.). The whole hydraulic package of a cooling system: open and closed circuits, pump skids, sectional and welded tanks, a glycol top-up station, a water treatment panel. Flow, head and NPSH calculations, tank volumes, glycol; schematics, piping, siting and controls.

APM007. NCT controls and control panels (82 pp.). The control system of a chiller plant: control levels, sensors and actuators, power supply and the panel, plant control logic, protocols and BMS integration, design package, commissioning and acceptance. Here the plant is treated as a whole: how machines, pumps and heat exchangers work together.

Key takeaways

Absorption chillers and the cooling tower. A single-effect absorption chiller loads the cooling tower twice as hard as an electric chiller of the same capacity. Five percent water in the steam means four percent less cooling and a broken valve seat. The boiler house sees an absorption chiller start-up as a jump in steam demand.

Cooling tower water balance. Make-up and blowdown depend on the cycles of concentration, but beyond six cycles the gain is small. The required tower characteristic rises more and more steeply as the approach, how much warmer the leaving water is than the wet bulb, gets smaller. Nobody will confirm an approach below 2.8 K: CTI certifies the thermal performance of cooling towers only within those limits.

Chilled-water hydraulics. In the pressure drop of the design loop, pipes account for about a quarter and equipment for the rest. With a 2 K hysteresis, every doubling of the capacity step doubles the system volume you need. A buffer tank works only with flow passing through it.

Absorption heat pumps. In a type 1 heat pump, 1 kW of expensive heat plus 0.7 kW of waste heat gives 1.7 kW of hot water. The temperature lift of one stage is limited: "from 30 straight to 120" will not work. The benefit is counted over the months when both the source and the consumer exist at the same time, not by installed capacity.

Dry coolers. The closer the fluid temperature is to the air temperature, the faster the unit surface grows: a 10 K difference is the base, 6 K needs twice the surface, 4 K four times. An intermediate plate heat exchanger between the dry cooler and the chiller condenser adds 2 to 4 K, a second pump, a tank and make-up.

Pump stations. In the head of an open-circuit pump station, static height and the condenser make up half, pipes about one eighth. The duty point should sit within 70 to 120 % of the best-efficiency flow. The strainer is calculated at the point when it needs cleaning, not clean; NPSH is checked in the worst case: warm water, low level, a clogged suction screen and one pump running instead of two.

Controls and panels. Hard wiring is for what must always work, the bus is for what is useful to know; losing the link to the upper level does not stop the plant. For one 22 kW pump, peak current differs sixfold depending on the starting method. On a cable run longer than 100 m, the cross-section is dictated by voltage drop rather than heating. A flow meter needs straight runs of 10 D upstream and 5 D downstream.

The working figure comes from the manufacturer. Figures in the guides come from NCT and Thermax catalogues, Russian building codes, CTI and ASHRAE standards and our own projects. For a specific design, the working figure comes from the technical proposal for the model at your operating point; we issue it free of charge based on a completed data sheet.

Who is it for?

• HVAC, recirculating water and mechanical design engineers: all seven guides, above all the calculations, schematics and piping.

• Controls and electrical design engineers: APM007 and the controls sections of every guide.

• Chief project engineers, chief engineers and energy managers on the owner side: the first sections of each guide (do you need the machine, and which one) and the typical mistakes.

• Reviewers and owner's supervision engineers: the sections on Russian codes, typical mistakes and the final checklists.

FAQ

Where should I start if the project is a complete chiller plant?

Start with the guide for the main machine: APM003 for chillers or APM001 for absorption chillers. Then APM002 or APM005 for heat rejection, APM006 for pumps, tanks and glycol, and APM007 for plant controls.

Can I put the figures from the guides straight into a design?

The figures in the guides are for checking your calculation. The working figure for a design always comes from the technical proposal or data sheet for the specific model at your operating point. If you are not sure a rule fits your site, check with your lead engineer or with our engineer: asking is professional.

How does the heat pump guide differ from the absorption chiller guide?

A heat pump is built from the same vessels as an absorption chiller. So APM004 does not repeat steam, hot-water and gas piping, the flue, plant room layout or pressure equipment codes; those are covered in APM001. APM004 focuses on waste heat sources, temperature lift, heat balance, connection schemes and annual benefit.

Related articles

• What is a chiller? How it works, main parts, layout and types

• How to choose an industrial cooling tower: open, closed or hybrid

• Absorption heat pump: how to recover waste heat from 25–50 °C water

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