Overview of Heating Systems

The basic overview of the system we install with a few pros and cons
 

OUTPUT TYPES

• Radiator based systems
  • Typically a radiator system would run with around 65°C to 72°C water temperature
    • Lends itself to a high temperature energy source such as a Boiler or Log-burner also some of the newer more exotic refrigerant Heatpumps.
  • The Radiator output is typically 50% thermal radiation and 50% natural thermal convection
  • Radiators are usually sized according to the thermal loses in a given room
  • Radiators are quick to heat up when the system comes on.
  • Very good response time with changes in room conditions
  • Output is mechanically controlled based on desired Air Temperature on the radiator valve
  • Slightly more efficient use of energy vs Underfloor or Fan Coils
• Underfloor based systems
  • Typically an underfloor system runs with around 36°C to 40°C water temperature
  • Ideal for standard Air to Water or Water to Water Heatpumps and high efficiency boilers. Driving from a logburner is possible but not ideal
  • Output is typically 90% Thermal radiation and 50% natural convection
  • Would usually utilize a slab limit temperature of approx. 28°C to prevent overheating of the Slab and damaging overlay floor coverings.
  • For best results pipe would be installed in the Concrete slab (or possibly a screed) no more than 35-50mm below the surface, typically tied to the Wire mesh.
  • Screed systems tend to give a much better response curve to changing conditions – in-slab tend to give better thermal mass characteristics but a slightly slower overall
    response.
  • Needs a good control system to help with slow warm up cycles.
  • Slightly less efficient than a Radiator system, however this is in part due to Slab losses which have been somewhat addressed in the newer H3 revisions to the building code.
• Fan Coil Units
  • Typically used in the same network as a Radiator system – i.e. Kitchen Toe space under cabinetry or larger units in rooms with restricted wall space
  • Output is 100% forced convection (Fan) – i.e. no thermal radiation.
  • Performs in the same way as a high wall spit heatpunp but as part of a bigger system.
  • Very fast thermal output, however (as with traditional heatpumps) only really heats the Air in a room – i.e. quick to heat when it comes on but also quick to cool off when it turns off.
  • Quite expensive where compared to Radiators

 

HEAT SOURCES

• Heatpumps
  • A Heatpump is a unit that transfers energy from one place to another, and, sort of concentrates it. There are 4 main types, Air to Air, Air to Water, Water to Water and Gas Absorbtion.
  • With Air to Air & Air to Water Heatpumps their efficiency greatly depends on the outdoor ambient condition – the colder it gets outside, the less energy is contained in the Air and the harder the unit has to work – so the efficiency drops dramatically the colder it gets outside, down to the point where the outdoor unit freezes and needs to run a de-ice cycle (during which it is negatively efficient). Typically efficiency would be in the 90% - 400% range.
  • Water to Water Heatpumps would normally have a pipe network buried in a field or large garden – they would be buried at a depth where the ground temperature is stable all year (typically 1.4 – 1.8m deep is approx. 14°C). The energy in the ground loops is more stable than the energy in the air so typically the performance would be less variable over the course of a heating season.
  • As almost all NZ heatpumps do not utilize combustion are no restrictions under Clean air policy (NESAQ), however in some regions there are by- laws for connecting large non-inverter heatpumps to the electrical grid.
    • Air to Air Heatpumps absorb energy from the outside ambient air – transfer that energy to a refigerent, move the refigerent to an indoor unit(s) and then transfers it back to the indoor Air This would be your typical High Wall Split or Console unit.
    • Air to Water Heatpumps in the same way absorb energy from the outside ambient air and again transfer it to a refrigerant – however instead of transferring the energy to the indoor air it transfers it to a water system that can then be used to drive a heating system such as in slab underfloor or radiators.
    • Water to Water Heatpumps absorb energy from the ground pipe network (or large body of water) and as with the above examples transfers it to your indoor water network.
    • Gas absorbtion Heatpumps utilise combustion to drive the process instead of an electric compressor – they typically use considerably less electrical energy than traditional heatpumps but are more suited to medium and large scale applications - these are gaining popularity in commercial buildings in Europe.
• Boilers
  • A boiler is a unit the uses combustion as its primary source of energy – there are 3 main types of Boiler – Gas fuelled Boilers, Liquid fuel boilers and Solid fuel Boilers.
  • Boilers typically need regular maintenance (every 1 to 2 years) to stay at peak efficiency.
  • Gas & Liquid fuelled Boilers tend to run it the 90 to 97% efficiency range and solid fuel boilers tends to operate in the 70 to 90% range.
    • Gas Boilers would normally use either Natural Gas or LPG as the fuel – they are usually wall hung and would be the cheapest option for boiler – however, the running cost is extremely high especially on LPG (although this is more to do with the cost of the fuel over the efficiency of the boiler). Virtually all are fully clean air approved as they are very clean burning.
    • Liquid fuel boilers (domestic) would typically use Kerosene or Diesel as the fuel – a typical domestic boiler would be the size of a single kitchen cabinet, and usually have an efficiency in the 92-96% range. Diesel still gives an excellent price per kilowatt hour figure, meaning it is still a very good option for most systems that need a boiler. Virtually all are clean air approved however, they do need maintenance or can become dirty over time. Waste oil boilers are available and can be clean burning if set up correctly – not typically for domestic applications.
    • Solid fuel boilers would be Wood, wood pellet or coal even but still utilize automated combustion (although some wood boilers still require manual loading). These are usually in a more complex system than gas or oil boilers but typically have the best running cost figures, especially if you have access to your own wood. A number of wood and wood pellet boilers are now clean air approved and can be installed in urban environments.
• Log Burners, Kitchen ranges & Open Fires
  • A log burner is any fire with an enclosed fire box (i.e. it has a door on the front) typically installed in the main living area of a home. Outputs can vary from a few kilowatts through to 40 or 50kWh into the room – heat is emitted from both the Fire and Flue pipe. Almost all of the energy is emitted as thermal radiation however this typically drives a certain amount of secondary convection. Clean Air standards have pushed many manufacturers to produce low emission burners (LEB's) and ultra low emission burners (ULEB's), these units predominantly utilize gasification to achieve the clean air standard by increasing the fire box temperature or more commonly drawing the flue gasses through the ember bed.
  • Heating Water - Wet backs are usually bolt in appliances that contain water to absorb the fire box heat and transfer it to water. In a ULEB fire this can hamper the gasification process which leads to many manufacturers reducing the output of the Wetback to keep the firebox temp as high as possible. Most ULEB fires would have a max wetback size of 2 to 4kWh, enough to heat the hot water cylinder but little else. Some larger fires have a full water Jacket around the fire box (similar to a boiler) however, these tend to be imported and not usually clean air approved (rural only). The big fires usually pump about 25kWh into the room and a further 15-20kWh into the water jacket, which is good for heating domestic hot water and a heating system.
  • Kitchen Ranges – These are very rarely clean air approved and although exempt from clean air standards in the building code most are restricted in urban areas by district plan implemented by unitary authorities (such as ECAN), this would normally restrict them to 2Ha+ sections or rural environments. A typical kitchen range would by something like a Rayburn or a Homewood (NZ made) and would supply heat, cooking facilities and the production of Hot Water for a cylinder and heating system.
  • Open Fires – As an open fire cannot regulate its primary combustion air it is not going to ever achieve clean air status, they are also notorious for allowing lots of heat to escape up the flue. Hence most have an efficiency below 70%. They are a nice addition to a home but typically will not have a wetback option so would normally be used for ambience rather than performance.
• Solar Hot Water Systems
  • Solar collectors are still an excellent addition to any system, most stand alone solar water systems (that have been sized & installed correctly) would typically provide approx. 80-90% of annual hot water production. Bearing in mind that Hot Water pruduction is usually around 40 to 50% of an average homes energy consumption, a solar water collector is extremely effective at lowering overall energy purchased for the home.
  • Summer v Winter – in Canterbury a Solar Water collector would provide all hot water between the Spring and Autumn Equinox and would only need to be partially topped up through the winter months. Most collectors also have the ability to control the electrical element so there is almost no risk of running out of hot water on cold, cloudy days.
  • As part of a our heating systems – in many cases we utilize our heating systems to provide Domestic Hot Water production, however, in the summer months when the heating system is not being used a solar collector can take over with hot water production. In these systems our customers typically never have the immersion element used all year.