Intelligent plantrooms contain multiple heat production appliances, often connected to more than one fuel source, such as gas and electricity. Typical examples would be gas CHP, gas & electric boilers, electric heat pumps and connections to waste heat sources.
Hybrid Energy Centres react to the prevailing conditions such as availability of low cost and low carbon energy from renewables and automatically prioritise the most appropriate energy source to keep the operational expenditure (OPEX) and carbon footprint as low as possible.
Where a gas connection is available, CHP offers significant CO2 footprint and cost savings in new-build and existing buildings.
Using a high efficiency, low NOx emission gas engine, CHP’s generate low carbon, low-cost electricity at the point of use and on-demand. Unlike intermittent renewables, CHP can react to the buildings consumption of electricity and modulate generation in real-time according to site loads, tariff signals and grid carbon intensity. Hence, CHP saves carbon and costs by displacing the consumption of grid electricity.
Inherently waste heat is produced as a by-product of generation. This ‘free’ heat is captured as heated water and is used within the building to reduce the output of the boiler and reduce the boiler’s consumption of gas or electricity.
In a hybrid energy centre, heat pumps are also a customer for CHP electricity and the two appliances become consumer and producer within a Prosumer building. This helps to protect the grid from some of the impact of large-scale electrification of heat production.
In a Hybrid Energy Centre, Heat pumps are sized to provide the maximum share of energy (kWh) but are not sized to the peak building load (kW) as this is extremely expensive and results in over-sized, under-utilised appliances. Hence, cost effective peak capacity should be provided by boilers.
Heat Pumps use a vapour refrigeration cycle to generate hot water by harvesting energy from a lower temperature source. This source is generally air or water, and could be from the ambient air, exhaust air, river water, bore hole, mine water and many others.
The input energy is electricity to power compressors and fans if the source is air.
Efficiency is the ratio of heat output divided by electricity input, known as COP (coefficient of Performance).
Refrigerants can be synthetic, but there is an increasing drive towards natural refrigerants such as CO2 and Ammonia as these are not damaging to the environment and do not contain embodied carbon. Their global warming potential (GWP) can therefore be 0 or 1.
In an all-electric energy centre, electric boilers provide cost effective peak capacity to support an optimised heat pump installation.
Electric boilers with 7, 15 or 30 operating stages turn down to a single stage of operation and modulate in small increments to top-up the output from heat pumps.
Boiler capacity can be large, but its share of energy should be as small as possible to maintain a low carbon footprint and a low OPEX. Per kW, electric boiler capital expenditure (CAPEX) is a fraction of an equivalent capacity heat pump.
As electric boiler operation is deliberately intermittent or as a stand-by plant, long term safety and reliability are important considerations.
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