NCT controls, water treatment and pump skids for absorption chillers

An absorption chiller controls only itself. It does not command the cooling tower, the bypass, the pumps or the fans: it sends signals to start and stop the pumps and a permissive for the cooling tower. The plant logic is handled by the control system. If there is no control system, or it was written without the chiller in mind, the interfaces break: the cooling tower, the engine jacket water, the power supply.

What does the plant control system include?

Three levels.

Chiller controller. A Thermax lithium bromide absorption chiller is controlled by a programmable controller with a touch panel. The operator sees setpoints, parameters, statuses, alarms and the event log. The chiller connects to the building management system via Modbus; at the Syry Kubani cheese plant it is Profibus with a Siemens controller.

Panels and plant logic. Interlocks: no chilled water means the cooling water must stop within one minute. Start-up: the chilled water pump first, the cooling water pump 15 seconds later, the cooling tower in bypass, the heating medium ramped up smoothly over 10 minutes to avoid thermal shock. Shutdown: the heat source closes, the chiller goes into the dilution cycle, the cooling water stops after about a minute, and the chilled water pump stops last.

Remote monitoring. A control system with online monitoring sends the parameters to the control room. At the Teplichnoye greenhouse complex, such an NCT system works together with the absorption chiller and cooling towers. With remote monitoring, any deviation from normal operating modes reaches the specialists as an alert: details on the service page.

Which pump skids does an absorption chiller need?

Three water circuits: heating, chilled at 7/12 °C, and cooling at about 27/32 °C. Each has a duty and a standby pump, a flow switch, balancing valves and air vents. Flow through the evaporator is constant; variable flow is handled in the secondary circuit. The pump skids are made by NCT.

Thermax's hydraulic requirements are as follows: a modulating three-way valve sits on the hot water inlet, a check valve with a bypass on the return, and isolation valves at the chiller. If the valve is installed on the hot water outlet, that violates the manual and leads to a warranty dispute. That is why the valve is written into the scope of supply in advance.

Why water treatment?

Scale 1 mm thick takes away about 14% of absorber capacity and adds up to 20% to energy consumption. Oxygen in the hot water circuit destroys the generator tubes. Thermax sets water requirements for all three circuits: pH 7.0–8.5, chlorides, hardness, iron, free chlorine and other parameters, according to a table for each tube material.

Water treatment is selected based on an analysis of the makeup water, not from a template: softening, dosing, reverse osmosis depending on the analysis results, automatic blowdown by conductivity, sampling points on all three circuits. Sites use NCT W0C, W2C and W3C units; which one you need is determined by the water analysis.

A cost example for a 5 MW data center: a water treatment unit costs about RUB 400 thousand, chemicals about RUB 70 thousand per year. This is a model calculation, not an offer.

How does this connect to the rest of the equipment?

Controls, pumps and water treatment link the chiller to the NCT cooling tower, the dry cooler and the chiller. We design all of it together for your scheme: design. For mistakes at the interface between the engine and the cooling side, see why trigeneration does not pay off.

If you want us to check what controls your plant, submit a request for a feasibility study or try the calculator. NCT equipment: nc-t.ru.