Industrial cooling systems work hard to keep process equipment, manufacturing lines and data centres within safe operating temperatures. In doing so, they generate significant amounts of heat as a byproduct – heat that is typically expelled into the atmosphere and lost entirely. A heat recovery system captures that heat before it disappears and puts it to practical use on site.

This guide explains what a heat recovery system is in an industrial and process cooling context, not domestic ventilation. We focus specifically on heat recovery from industrial chillers, how it works, what the recovered heat can be used for, and the practical factors that determine whether it is the right solution for your site.

Key Takeaways

  • A heat recovery system captures waste heat generated as a byproduct of industrial cooling and redirects it for useful purposes such as space heating.
  • Heat recovery from chillers works differently depending on chiller type – air-cooled systems use ducted hot air; water-cooled systems divert heat via an LTHW ring main.
  • Recovered heat is typically used for space heating, radiators, fan heaters and air handling units.
  • Heat recovery reduces reliance on fossil fuels for heating, cutting energy costs and carbon emissions.

What is a heat recovery system?

A heat recovery system is a mechanism for capturing the heat produced as a by-product of a cooling process and redirecting it for practical use, rather than expelling it into the atmosphere as waste.

In industrial process cooling, the source of that waste heat is the chiller condenser. Every chiller, whether air-cooled or water-cooled, must reject heat to maintain the refrigeration cycle. The quantity involved is substantial. For every 100 kW of cooling a chiller delivers, approximately 133 kW of heat is produced at the condenser. This approximate ratio reflects the physics of the refrigeration cycle: cooling capacity plus the heat generated by the compressor equals total condenser heat rejection. The actual figure varies depending on the specific chiller, its coefficient of performance, and operating conditions – but the 100:133 relationship is a useful planning approximation.

Without heat recovery, that condenser heat, roughly a third more than the cooling load itself, is wasted. With a heat recovery system in place, a significant proportion of it can be captured and used to heat factory spaces, offices or process water, reducing the site’s reliance on gas boilers or other fossil fuel heating systems.

How does heat recovery work in a chiller system?

The method used to recover heat from a chiller depends entirely on whether the unit is air-cooled or water-cooled. These are two fundamentally different configurations that require different approaches.

Air-cooled chiller heat recovery

An air-cooled chiller rejects condenser heat by passing refrigerant through an air-cooled coil and blowing ambient air across it with fans. Typically, the hot air generated is vented directly into the atmosphere.

With heat recovery, the warm discharge air from the condenser is ducted into the building rather than expelled outside. A damper system controls when this occurs. On simpler installations, the damper is manually operated. More sophisticated setups use a temperature-controlled automatic damper that opens only when the internal space requires heating – closing again once the target temperature is reached or when the outside conditions make it inefficient.

This approach suits smaller sites, factories or warehouses that do not have a centralised heating circuit. It is most effective in winter and shoulder seasons when there is a genuine heating demand. In summer, the recovered heat simply is not needed, so the damper stays closed and the system operates as normal.

Water-cooled chiller heat recovery

A water-cooled chiller uses a secondary water circuit, rather than air, to carry heat away from the condenser. In a standard installation, that circuit runs to a cooling tower or dry cooler where the heat is rejected into the atmosphere.

Heat recovery from a water-cooled chiller works by diverting some or all of that secondary circuit flow through a low temperature hot water (LTHW) ring main rather than directly to the rejection unit. The LTHW circuit then distributes the recovered heat around the site, supplying radiators, fan heaters, air handling units (AHUs) or pre-heating process water.

One important caveat: the heat recovered from a chiller condenser is low-grade hot water, typically in the range of 35-45 degrees Celsius. This is suitable for space heating circuits, fan heaters and some AHU coils, but it is not appropriate for domestic hot water supply, which requires higher temperatures to meet Legionella control requirements.

What can recovered heat be used for?

The most common application is space heating. Factories, warehouses and industrial units often have significant heating demands in winter, and condenser heat is well-suited to meeting them cost-effectively. Recovered heat can supply:

  • Radiators and panel heaters on an LTHW ring main
  • Unit heaters and fan heaters distributed across large floor areas
  • Air handling units for tempered ventilation supply
  • Pre-heating of process water where elevated temperatures are not required
  • Underfloor heating circuits on low-temperature systems

In our experience, the best results come from sites with a clear, consistent winter heating demand that runs in parallel with year-round cooling. As an example, a large pharmaceutical and chemical manufacturing site we worked with had a continuous process cooling requirement alongside a significant space heating load in a multi-building campus. Connecting the chiller condenser output to the existing LTHW ring main provided enough recovered heat to meaningfully reduce the site’s gas boiler consumption, with a measurable impact on both energy costs and carbon emissions.

Is heat recovery right for your site?

Heat recovery is not suited to every site or every cooling installation. Before specifying it, the following questions help determine whether it is a viable and worthwhile option:

  • Does your site have an existing heating demand that runs concurrently with your cooling load? Heat recovery delivers greatest value where heating and cooling needs overlap – typically process industries, manufacturing and logistics facilities.
  • What type of chiller do you have? Air-cooled and water-cooled systems require different heat recovery approaches. Confirm which applies before assessing viability.
  • Do you have an LTHW ring main or space heating infrastructure in place? Water-cooled heat recovery works best when an existing distribution circuit can accept the recovered heat.
  • What is the condition of your existing heating pipework? Older systems may require assessment before connection (see the next section).
  • Are you also considering free cooling? If so, this affects your design options – see the section on mutual exclusivity below.

If you are unsure whether heat recovery is suited to your site, an energy assessment will identify the potential and indicate likely payback timeframes. Our team carries out site surveys specifically for this purpose.

What to check before connecting heat recovery to an existing heating circuit

Connecting heat recovery equipment to an existing LTHW heating circuit is not always straightforward – particularly on older industrial sites.

Heating circuits installed 15-20 years ago are commonly built from mild steel pipework. Over time, corrosion produces rust particles and other contaminants that accumulate in the circuit. When a new heat recovery heat exchanger is connected to such a system, those contaminants can quickly migrate into the chiller condenser or heat exchanger, causing fouling and potentially serious damage.

The correct approach is to isolate the heat recovery heat exchanger from the old circuit using an intermediate heat exchanger, so that the two water circuits never mix directly. Additional filtration – typically a magnetic filter or strainer – should also be installed on the return to capture any particulate before it reaches the new equipment.

We encountered this issue on a project at a chemical manufacturing site, where the existing heating infrastructure was well over a decade old. The pipework contamination risk was identified during the site survey, and heat exchanger isolation plus filtration was specified as part of the installation design. Without that assessment upfront, the outcome would have been a blocked condenser and an expensive early failure.

This is one of the reasons a professional site assessment is essential before any heat recovery installation – not just to size the equipment, but to identify the condition of the circuits it will connect to.

Heat recovery and free cooling: why you can’t have both

Heat recovery and free cooling are two distinct energy efficiency strategies for chiller systems – and they are mutually exclusive in a water-cooled installation.

Free cooling uses low ambient temperatures to pre-cool the secondary circuit before it reaches the chiller, reducing the compressor load and cutting energy consumption. Heat recovery uses the same secondary circuit to carry condenser heat to the site’s heating distribution system.

Both approaches compete for the same circuit. Designing the system to favour heat recovery means the secondary circuit is configured to deliver heat to the LTHW ring main. Designing it for free cooling means the circuit is configured to exploit ambient conditions for pre-cooling. The two objectives pull in opposite directions, and attempting to run both simultaneously undermines the performance of each.

This is a design-stage decision. If you are evaluating both options, it needs to be resolved before installation commences. Our free cooling systems page covers that option in more detail if you are comparing the two.

When does heat recovery deliver the most value?

Heat recovery provides maximum value in winter and the shoulder seasons – the periods when your site’s cooling system is running and there is a genuine demand for heating at the same time.

In those periods, every kilowatt of heat captured from the condenser is a kilowatt you do not need to generate with a gas boiler or electric heater. The financial and carbon benefit is direct.

In summer, the system continues to cool your process effectively, but the recovered condenser heat may not be needed for space heating. On air-cooled systems with automatic dampers, the damper simply stays closed and the heat is vented as normal. On water-cooled systems, the heat recovery circuit can be bypassed. The chiller operates as it would without heat recovery in place.

Setting realistic seasonal expectations matters when calculating payback. A heat recovery system at a site with a strong winter heating demand and year-round cooling can deliver a compelling return. The same equipment at a site that runs cooling only in summer – with no concurrent heating need – will deliver far less value. An honest energy assessment, based on your actual site profile and operating hours, is the best way to establish whether the numbers work.

FAQ's

What is a heat recovery system?

A heat recovery system captures the heat generated as a byproduct of a cooling process – from a chiller’s condenser – and redirects it for useful purposes such as space heating or a low temperature hot water circuit, rather than expelling it into the atmosphere. In industrial settings, this means using heat that would otherwise be wasted to reduce the energy demand from gas boilers or other heating systems.

How much heat can be recovered from a chiller?

As a useful planning approximation, for every 100 kW of cooling a chiller provides, approximately 133 kW of heat is produced at the condenser. This figure is approximate – actual values vary depending on the chiller’s design, efficiency rating, and operating conditions. Without heat recovery, that heat is wasted. With heat recovery equipment in place, a significant proportion can be captured and used.

Can heat recovery be retrofitted to an existing chiller?

Yes – heat recovery can be retrofitted to both air-cooled and water-cooled chillers. A site survey is essential first, particularly to assess the condition of any existing heating circuits. Older mild steel pipework can introduce contamination risks that need to be managed through heat exchanger isolation and filtration before connection.

Is heat recovery the same as free cooling?

No. Free cooling uses ambient conditions to reduce the load on a chiller by pre-cooling the secondary circuit. Heat recovery captures condenser heat for redistribution around the site. In a water-cooled system they use the same secondary circuit, so they cannot both be optimised simultaneously – this is a design-stage decision that must be resolved before installation.

What type of chiller is best for heat recovery?

Both air-cooled and water-cooled chillers support heat recovery, but via different methods. Air-cooled units suit ducted hot air heating of factory or warehouse spaces. Water-cooled chillers suit sites with a centralised LTHW ring main, providing low-grade hot water for radiators, fan heaters and AHUs. The right approach depends on your chiller type and site heating infrastructure.

Ready to explore heat recovery for your site?

Our engineers carry out site surveys to assess the potential for heat recovery from your existing chiller installation – including a review of your heating circuits, system configuration, and estimated payback. We work with both air-cooled and water-cooled systems and handle the full design and installation process.

Find out more about heat recovery for industrial process cooling or contact our team directly to discuss your requirements.