Heat Recovery Units and Heat Recovery Systems
An Introduction to Heat Recovery Units and Heat Recovery Systems
As the name would suggest, heat recovery systems, which include heat recovery units are a means of providing essential ventilation to meet the requirements of ‘Building Regulations Part F, whilst minimising operational expenditure, power absorbed and consequent CO2 emissions. This is achieved by a combination of measures intended to recover energy carried in spent air extracted from buildings and using energy efficient technologies to optimise power absorbed.
The European Parliament have taken this subject so seriously that they have issued the Energy Related Product (ERP) directive, which in the context of ventilation units has legislated on the minimum efficiencies that must be attained and set milestone dates for implementation.
Reference is made to heat recovery systems because the heat recovery unit in combination with its associated ducting, grilles and controls constitutes a system and therefore correctly designing the associated services is essential to meeting the limitations of the directive. In particular, this refers to specific fan power; in other word the fan power absorbed in order to overcome the resistance to airflow at a given airflow rate for the system as a whole.
The ERP Directive
Also known as the ‘ecodesign directive’ the ERP directive has been incorporated into UK law as ‘The Ecodesign for Energy-Related Products Regulations 2010’ as amended by Statutory Instruments and specifically in relation to Commission Regulation (EU) No 1253/2014 and 1254/2014.
Given that the purpose of ventilation units covered by the directive is for the exchange of air for occupied buildings, it should be noted that the regulation should not apply to a ventilation unit intended to be used in a building or part of a building not designed for human occupancy or where the primary function is not to replace spent air. The exception to this is where the ventilation unit is intended to replace air for another purpose such as equipment ventilation in which case the regulation still applies.
These Regulations apply to ventilation units where ecodesign requirements are to be implemented for those being introduced to the EU market or being put into service. All ventilation units of a proprietary or bespoke nature introduced to market or put into service from 1st January 2016 must conform to Commission Regulation (EU) 1253/2014 and 1254/2014.
Electric Motors for Fans
EU Commission Regulation No 640/2009 is already in effect and requires electric motors for ventilation units to meet the following legislative timetable.
From 1st January 2015:
Electric motors with a rated output of 7.5 – 375 kW shall not be less efficient than the IE3 efficiency level, or meet the IE2 efficiency level and be equipped with a variable speed drive (VSD). VSD types might typically be inverter or electronically commutated.
From 1st January 2017:
Electric motors with a rated output of 0.75 – 375 kW shall not be less efficient than the IE3 efficiency level, and be equipped with a variable speed drive.
Specific Efficiency Criteria
With a few exceptions, non-residential ventilation units shall meet the following which include heat recovery units for occupational ventilation from 1st January 2016.
- All ventilation units, (except dual use units) shall be equipped with multi-speed drive (MSD) or VSD.
- Electronically commutated (EC) fan motors are considered as equipped with VSD and thus fulfils the VSD requirement.
- All bidirectional ventilation units (BVU) shall incorporate a heat recovery method that meets or exceeds the minimum efficiency given for the particular method selected.
- A heat recovery unit forming part of a heat recovery systems shall have a means of thermal by-pass in order that unnecessary heat recovery does not have a detrimental impact on the thermal load of the building being served. This might be: (1) Summer by-pass damper for plate heat exchangers, (2) VSD for thermal wheels or (3) pump flow control for run-around coils.
- The thermal efficiency of run-around coils shall be a minimum of 63%. This efficiency is based on equal balance of supply and extract airflows and assumes that the circulating fluid is a solution of 25% ethylene glycol and 75% water.
- The thermal efficiency of plate type recuperative heat exchangers and thermal wheels shall be a minimum of 67%. This efficiency is based on equal supply and extract airflow rates.
- Fan efficiency for unidirectional ventilation units (UVU) to be minimum 62% if power absorbed is less than 30 kW
- Fan efficiency for UVU to be minimum 56.1% if power absorbed is greater than 30 kW
- Determination of specific fan power (SFP) is the electric power supplied to a fan and related to the internal pressure of all ventilation unit components (filters, heat recovery and related casing including flow entrance and exit) divided by the airflow expressed in m3/s under design load conditions. SFP value vary for differing heat recovery methods (run around coils, plate heat exchangers and thermal wheels). Manufacturer’s data shall confirm compliance with the required minimum SFP to confirm compliance.
- UVUs intended to be used with a filter have a limiting SFP of 250 W/m3.s.
Further to the above; specific ecodesign requirements for non-residential ventilation units will become more stringent with effect from 1st January 2018. For support and guidance in respect of current legislation and future changes please contact us directly.