Cascading boilers – something new for me

Cascading boilers (with my daughter)

Having now been involved with well over 20 biomasses i thought i understood the principals of biomass sizing and setup

  • Understanding how much heat the building needs (heat loss) and hot water needs?
  • Understanding the % balance between base load and peak load?
  • Getting the fuel right (can you get it to site and is it the right quality)?
  • Controlling the heat distribution?
  • How big does the boiler and buffer tank need to be?
The last one, the buffer tank is something i had grown accustomed to. The buffer tank is simply a well insulated tank of hot water tank helps meet any peak loads by sometimes being used in conjunction with the boiler or allowing the boiler to stay off when there is only a small amount of heat needed because the building can draw off the buffer tank. e.g. If you have a heat demand of 20kw (heating and showers in the morning) but the biomass is only sized to 15kw. the buffer tank stores this 5kw shortfall because it was charged up the night before and so the boiler and the tank combined meet this need. the last thing you want is a biomass boiler sized to meet the peak load because for a high percentage of its life it will only be running at half or to three quarters capacity. (wasting money, not running efficiency and cycling more often ( switching on and off)
So when the proposal came in for a cascading biomass system for two cottages at DyffrynCottage Gallery Mymbyr i was a bit surprised. Although we have experience with twin boilers such as the 150 and 300kw at Chirk castle they do have a small buffer capacity (6000ltrs) Dyffryn Mymbyr site now has twin biomass boilers to meet the 40kw peak load but can modulate down to 6kw for the heating (which it does not need to do because of the control systems) hot water is supplied via small hot water tanks which are charged by the biomass. 
12 months in and it’s working fine
  • One boiler acting as a backup for the other
  • No need for a large water tank loosing heat
  • has been bomb proof in terms of breakdowns
  • More expensive to install
  • Slightly higher maintenance costs (more than one boiler)
so overall we are please with the system and are seeing what it will do over the coming years. 
National Trust Green Energy in partnership with npower
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