Case Study:
CHP and district heating

Multi-apartment development achieves NZEB standards using natural gas

Supporting developers achieve NZEB standards with natural gas

The updated building regulations require new residential buildings to have a very high energy performance. The low amount of energy (nearly zero) that these buildings require should, to a significant extent, come from renewable sources produced on-site or nearby.

A combination of natural gas, CHP and heat pumps helped the Cosgrave Group meet all of the Part L 2019 (NZEB) building regulations on their multi-apartment development. We are committed to supporting developers who are dedicated to sustainable and energy efficient design but face challenges meeting stringent building regulation requirements.

If you wish to explore how you can achieve NZEB standards for your planned development and provide your customers all the benefits of natural gas, please contact us today for a free consultation.

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A2 rated apartments with natural gas

Bridgefield and Pappan Grove built by the Cosgrave Group are located in the centre of Northwood, Santry, close to Gulliver’s Retail Park. The development is comprised of three six-storey buildings and one five-storey building incorporating 250 apartments, which are built over a basement car park.

A district heating system comprising of central gas boilers, gas-fuelled combined heat and power (CHP) units and electric heat pumps, provides space heating and hot water for the entire development. The apartments have a BER rating of A2 and meet Part L 2019 of the building regulations, commonly referred to as Nearly Zero Energy Buildings (NZEB).

Challenge of multi-apartment developments

When specifying a new development's energy solutions, the improved number and variety of systems creates a dilemma for any developer. Ensuring that you "future proof" the development while keeping pace with ever changing customer preferences can be a challenge.

The use of new technologies is easier when you have the floor or roof space to install them, which most new, 3-bedroom semi-detached homes do. However, this is not the case for multi-apartment building developments where roof space is limited, and internal space is at a premium. New, more cohesive ways of thinking and working are required in order to meet the individual heating and hot water requirements of apartments, in a sustainable manner.

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Development features

  • Combined Heat and Power
  • Heat Recovery Ventilation
  • Excellent levels of air tightness
  • Two 1,500-litre buffer water cylinders
  • High levels of insulation with double-glazed windows

"The versatility of natural gas made Combined Heat and Power the most logical option."

Richard McElligott
Director, McElligott Consulting Engineers Ltd

System features

Combined Heat and Power

The CHP units run on natural gas to generate electricity on-site. The electricity generated is then used to power the heat pumps and some public lighting. This provides electricity at a significantly lower rate than grid electricity, saving the residents on energy costs. Generating electricity in this way also produces heat that is captured and used to generate space heating and hot water for all of the apartments.

Heat Recovery Ventilation

The Heat Recovery Ventilation (HRV) system is designed to remove stale air from homes and provide a constant supply of clean, filtered air. It operates by gently ventilating the property at a rate of about half an air change per hour, removing the stale air from the kitchen, bathrooms and toilets and extracting it to the outside.

Heating control

With the swipe of a finger on a smart phone, or even by SMS, the next generation Prepago heating control systems allows residents to control and monitor their apartment’s heating system remotely. Hot water is heated centrally and is available to all residents on tap. As a result there is a constant supply of hot water, thereby eliminating wasted energy. Residents only pay for what they use.

Building fabric

  ActualPart L 2019 (NZEB) requirement

Floor (W/m2.K):

0.14 0.18
Walls (W/m2.K): 0.16 0.18
Roof (W/m2.K):   0.16 0.16 (0.20 for flat roof)
Windows (W/m2.K): 1.40 1.40
Thermal Bridging Factor (W/m2.K): 0.08 0.15

Heating system: ≥90% efficient gas boilers in combination with CHP system

The district heating system in this development combines CHP, gas boilers and heat pump technology to meet the renewable contribution as set out under Part L 2019 of the building regulations. The gas boilers installed have a net efficiency of 94%. The CHP engines are 65% efficient (heat generation/condensing function) and 24% efficient (electricity production).

Ventilation: Mechanical ventilation throughout the home

These apartments contain double-glazed windows, which help with background ventilation, combined with a mechanical ventilation system and an air permeability of 3m3/(h.m2) at 50 pa. This exceeds the minimum TGD Part L requirement of 5m3/(h.m2) at 50 pa.

Renewable energy contribution: ≥20% of energy requirements

This development utilises a CHP system comprising of three micro CHP units, with thermal outputs of 14.7kW, in combination with three air-to-water heat pumps. Each electric heat pump is rated to 16kW output. The renewable energy contribution from this solution is the equivalent to over 20% of the buildings primary energy demand. This meets the renewable energy requirements of Part L 2019 of the building regulations.

Renewable gas ready

While carbon emissions reductions can be realised for developments using natural gas with hybrid heating systems, even more significant savings are coming down the road as we continue our journey to decarbonise home heating in Ireland with renewable gas.

Locally produced renewable gas is now flowing onto the gas network at our purpose built gas injection facility in Cush Co. Kildare. Once flowing at full capacity, it will be able to provide enough renewable gas to heat approximately 11,000 homes. A second gas injection facility is currently in the planning process for Co. Cork.

As the industry grows and more renewable gas flows through the pipes, home owners will benefit from even lower emissions without having to make any additional investment. No change will be required to the domestic heating systems as they are already compatible with renewable gas.

Performance coefficients

 Part L (2019)Actual

Carbon Performance Coefficient (CPC)



Energy Performance Coefficient (EPC)



Primary Energy Value (kWh/m2/yr)



Bridgefield case study - PDF

Book a free consultation

If you wish to explore how you can achieve NZEB standards for your planned development and provide your customers all the benefits of natural gas, please contact us today for a free consultation.

Book a free consultation