determine demand
The Carbon Trust’s Biomass Decision Support Tool (discussed within the next sub-navigation panel) is primarily intended for the detailed sizing of proposed biomass systems. However the first inputs which must be stipulated generate a heat demand profile for a broad range of selectable building types, including swimming pools and residential housing estates. This demand module operates independently of the biomass system sizing capabilities to follow, and may therefore be used with general applicability. For example, if a common consumer was looking into replacing their conventional fossil fuelled boiler with alternative renewable heat but was unsure as to the financial feasibility of doing so, a logical procedure would be to use the Biomass Decision Support Tool’s capacity to accurately estimate their annual heat demand and from this perform simple calculations centred on payments from the Renewable Heat Incentive (RHI).
There are a range of RHI calculators online which proclaim to perform similar functions to this demand module snippet of the Biomass Decision Support Tool, but none do so with the level of quantitative detail established through extensive simulations. And although the Biomass Decision Support Tool in the background is intrinsically detailed, it presents a very user friendly interface. For example, the common consumer will most likely use the “embedded demand calculator” function which although is almost definitely the least accurate method of generating a heat demand profile, it is the most user friendly. Indeed, the only parameters that have to be specified are:
There are a range of RHI calculators online which proclaim to perform similar functions to this demand module snippet of the Biomass Decision Support Tool, but none do so with the level of quantitative detail established through extensive simulations. And although the Biomass Decision Support Tool in the background is intrinsically detailed, it presents a very user friendly interface. For example, the common consumer will most likely use the “embedded demand calculator” function which although is almost definitely the least accurate method of generating a heat demand profile, it is the most user friendly. Indeed, the only parameters that have to be specified are:
- House type (detached, semi-detached, bungalow, ground floor flat, top floor flat etc.)
- House age (pre-1983, 1983-2002, 2003-2007, or post 2007)
- Number of bedrooms (1, 2, 3, 4, or 5)
- Number of houses of this type (if investigating a potential housing estate installation)
- Average daily hot water consumption (typically 2 kWh / person / day)
- Outdoor design temperature (range -3°C to 14°C)
Design Day
The design day is one chosen from archived climate data to represent the (almost) worst case scenario any heating system will have to encounter, and is therefore central to the actual design and sizing of such a system. Many dispute that the idea of designing a heating system based on the worst climatic conditions that have occurred over a prolonged time frame is both impractical and inadvisable. The system is inevitably over sized for the vast majority of its lifetime at firstly unnecessary capital expense to the owner, but also meaning the system will not operate at, or at least near to, its design capacity for a sufficient proportion of time to the detriment of overall operating efficiency. It may be more reasonable to design the system based on climatic conditions representative of the typical average, and in extreme cases allow for internal building temperatures to drop a little below the desired temperature, as this is shown to have insignificant impact on thermal comfort levels [1]. But it is highly subjective what level of risk is quantified in this idea, and therefore the current design day model should remain standard practice for the foreseeable future - it is the only way of providing constant supply to satisfy demand, where the implications on human health of, in this scenario, temperatures dropping below typical comfort levels is a risk that cannot just be mitigated against, it must be avoided.
The design day includes a wide range of climatic parameters including the barometric pressure, humidity levels, wind speeds etc. However, for the purpose of this study we are only concerned with the outdoor design temperature (sometimes called the winter design temperature), as it is sufficient to define the heating systems we are interested in. The outdoor design temperature may usually be defined as the temperature that is equaled or exceeded 97.5% of the three coldest months in the year. For the purpose of this study, we define it as the temperature that is equalled or exceeded for 99% of the entire year, although any difference between these two methods is negligible [2]. Great care must be taken when defining the outdoor design temperature, as the sizing and thus achievable performance of a system is heavily dependent [3].
The design day is one chosen from archived climate data to represent the (almost) worst case scenario any heating system will have to encounter, and is therefore central to the actual design and sizing of such a system. Many dispute that the idea of designing a heating system based on the worst climatic conditions that have occurred over a prolonged time frame is both impractical and inadvisable. The system is inevitably over sized for the vast majority of its lifetime at firstly unnecessary capital expense to the owner, but also meaning the system will not operate at, or at least near to, its design capacity for a sufficient proportion of time to the detriment of overall operating efficiency. It may be more reasonable to design the system based on climatic conditions representative of the typical average, and in extreme cases allow for internal building temperatures to drop a little below the desired temperature, as this is shown to have insignificant impact on thermal comfort levels [1]. But it is highly subjective what level of risk is quantified in this idea, and therefore the current design day model should remain standard practice for the foreseeable future - it is the only way of providing constant supply to satisfy demand, where the implications on human health of, in this scenario, temperatures dropping below typical comfort levels is a risk that cannot just be mitigated against, it must be avoided.
The design day includes a wide range of climatic parameters including the barometric pressure, humidity levels, wind speeds etc. However, for the purpose of this study we are only concerned with the outdoor design temperature (sometimes called the winter design temperature), as it is sufficient to define the heating systems we are interested in. The outdoor design temperature may usually be defined as the temperature that is equaled or exceeded 97.5% of the three coldest months in the year. For the purpose of this study, we define it as the temperature that is equalled or exceeded for 99% of the entire year, although any difference between these two methods is negligible [2]. Great care must be taken when defining the outdoor design temperature, as the sizing and thus achievable performance of a system is heavily dependent [3].