Medium voltage electric steam and hot water generators for district heatingNovember 17, 2022
The electrification trend has spread beyond automobiles and is now moving into district heating applications with a focus on eliminating or supplementing fuel fired systems. Many district heating systems are fuel fired using coal, natural gas or fuel oil, and the heat produced in these systems is used to create steam and hot water which is routed to various buildings on a heating loop. Today, municipalities, utilities and companies are focusing on proactive approaches to reducing their carbon footprint, either due to the operational advantages or due to new regulations. In addition, stakeholders are demanding companies and institutions implement realistic decarbonization plans, further motivating the move away from fuel fired district level heating systems.
Today, there is a simple alternative to traditional fuel fired district heating systems that is cost competitive and more efficient. District level electric heating systems have become more efficient and cost competitive, both in terms of retrofits to existing systems and new system installation. Companies and institutions who want to decarbonize and move to a more operationally efficient heating system should consider electric district heating as a viable alternative. This guide will examine the advantages of district heating systems and the types of
electric heating systems end users can expect to be available from vendors, as well as the performance that can be expected in best-in-class installations.
Electric district heating system options
District heating involves distribution of heat to multiple commercial and residential buildings from a central location. Heat is carried by steam and hot water, which is generated at a boiler site, distributed throughout the local area, and brought back to the boiler location to be reheated and circulated. Local boilers at building entries may also be used for additional heating of incoming steam, which would typically be provided by burning natural gas.
Electric heating carries several important practical advantages for organizations beyond meeting compliance requirements and decarbonization goals. For example:
- Centralized electric heating allows for using existing steam and hot water distribution system
- Electric allows point of use installation with controlled power input and less waste
- Building operations are simplified as there is no fuel to monitor or manage
- Maintenance is much simpler as there are no combustion controls to adjust
- Electric systems are easier to upgrade or replace at end-of-life
- Renewables are directly integrated into the system
- Electric heaters conserve energy since they are much more efficient
The efficiency of electric heating systems is an important point to consider when comparing newer fuel fired systems. According to the U.S. Department of Energy, the efficiency of older fuel fired systems ranges anywhere from 56% to 70%. Electric heating systems easily exceed 98% thermal efficiency. Given the higher efficiency and other benefits of electric heating, it makes much more sense for facilities to replace their older fuel fired systems with newer electric systems.
In general, there are two types of electric heating systems that offer an alternative to fuel fired district heating systems: electrode boilers and resistive heaters. The two systems are similar in terms of operation, but they carry different operational and maintenance concerns that should be addressed when designing a district level installation.
An electrode boiler works by passing an alternating current directly through water to provide heat and generate steam or hot water. The inherent resistance to electric current directly heats water, with the final water temperature being proportional to the applied current. These systems can scale to satisfy higher demand in district level installations.
While electrode boilers come with all the advantages listed above, there are several drawbacks in their use as a primary heating system, and they require some specialized management and maintenance to ensure maximal operating lifetime. In particular, these systems can experience:
- Electrical conductivity due to poor water quality
- Foaming inside the boiler vessel, which will reduce the power output
- Scale deposition on electrodes
- Corrosion and fouling of spray nozzles, as well as electrical power insulators
- Moving parts, including critical circulation pumps that must be maintained and replace on a regular basis
- Complex pressure and temperature control with wide deadband
It’s important to note that these boilers can provide very high capacity with power output reaching as high as 60 MW. However, with these systems being complex, they tend to carry higher investment and maintenance costs than resistance heaters, making them a better option for very large-scale installations with high voltage available. In contrast, resistance heaters operating at low or medium voltage are an excellent option for district level installations.
A resistance heater creates steam and hot water by transferring heat from a resistive element into water via conduction and subsequent convection. Resistance heaters are much simpler than electrode boilers in terms of system components, control systems and ongoing maintenance. They have virtually no moving parts other than valves, and the control system for these heaters is much simpler and more accurate. Because they do not involve running a current through water, electrolytic reactions between metals and dissolved salts do not occur, and the water quality or scaling problems found in electrode boilers are prevented.
Some of the major advantages of resistance heaters include:
- Very little water treatment is required, and DI or de-min feedwater sources can be used
- Control is based either on outlet pressure or temperature with fast response time and tight deadband
- Minimal maintenance is required as the systems have no internal moving parts
- Electrical connections are isolated from the internal boiler vessel
- Operation at low and medium allows flexibility with power supply
Corrosion resistance can be provided by an appropriate sheathing material (such as Incoloy) on the heating elements inside the boiler vessel. Although power output can be lower than high-voltage electrode boiler systems, the up-front investment cost per kWh generated and the maintenance costs accrued over time can be much lower. This makes low voltage and medium voltage systems much more attractive for district heating applications. When selecting a resistance heater, the operating voltage is an important factor as low-voltage systems can differ greatly from high voltage systems in terms of performance at the district level.
Why Chromalox DirectConnect medium voltage electric heating?
In general, bringing an electric heating system on premises contributes to an organization’s net zero goals and is a key part of regulatory compliance. Compared to fuel fired systems, electric heating systems are much less complex, virtually 100% efficient, and they carry much lower installation and maintenance costs throughout the life of the system. In terms of decarbonization, these systems eliminate both Scope 1 and Scope 2 emissions* created by fuel fired systems. They can also integrate easily into legacy infrastructure with off-the-shelf components or customized solutions provided by system vendors. Other advantages of medium voltage installations include the elimination of costly step-down transformers, reduced installation labor hours compared to low voltage systems or electrode boilers, and fewer conduit runs and wired circuit requirements to implement these systems.
End users need to determine whether they will implement a low, medium or high voltage system for their heating solution. In terms of costs, efficiency and power output, medium voltage systems are an optimal option compared to low or high voltage systems. The table below provides a summary comparison of low and medium voltage electric heating systems. For district level installations, medium voltage is a superior option given its installation and maintenance costs benefits.
Chromalox DirectConnect medium voltage electric steam and hot water generators
Chromalox’s DirectConnect medium voltage electric heating solutions operate up to 7.2 kV and 10.9MW with virtually 100% efficiency. 450 PSIG standard designs are available, and custom designs can be procured operating at up to 1,000 PSIG. These electric heaters can be paired with control systems that connect directly to the local building management system (BMS) and communicate in the native BACnet language. Chromalox provides the required switchgear and power control assemblies which connects directly to the medium voltage power supply for easy onsite electrical installation.
This class of systems provides important reliability and operational advantages over comparable low voltage solutions, with medium voltage systems having longer lifetimes and higher reliability. In addition to greater reliability compared to low voltage systems, these medium voltage systems provide a factor of 8 to 10 times reduction on installation costs compared to fuel fired systems.
Superior industrial partnership
Working with Chromalox provides significant advantages over other firms offering electric heating solutions for large campuses, as well as advantages over fuel fired systems. Companies looking to decarbonize, reduce their operating costs and achieve lower costs for new system installation can look to Chromalox to provide a tailored solution with custom built or off-the-shelf components. Chromalox heating and control systems can also communicate with an existing BMS application, and they can be installed with limited modifications to existing boiler facilities if needed.
Chromalox provides sustainable products for the building and construction industry with a proven track record of engineering success. The applications engineering team at Chromalox brings proven experience designing electric district heating systems that meet performance specifications, regulatory and code requirements, and cost targets. Chromalox products and solutions provide high efficiency heating, monitoring and system control to a BMS with high reliability net zero heating.
Chromalox, a division of Spirax-Sarco Engineering, provides custom and off-the-shelf district-level electric heating solutions. Chromalox provides custom engineered electric heating solutions for manufacturing facilities housed on large campuses, including equipment and site engineering services. Chromalox invented the industry over 100 years ago and continues to service customers with industry leading design and engineering experience.
To begin the process of implementing a district electric heating system, either as a retrofit or a new installation, the end user can first engage with a design firm to develop specifications on system size (voltage, power output). End users can then work with the application engineering team at Chromalox to select off-the-shelf components and create a custom system design. Visit the Chromalox website for more information.