Heat Load calculation in term of HVAC

Heat load or heat gain A building or room gains heat from many sources. Inside occupants, computers, copiers, machinery, and lighting all produce heat. Warm air from outside enters through open doors and windows, or as ‘leakage’ though the structure. However the biggest source of heat is solar radiation from the sun, beating down on the roof and walls, and pouring through the windows, heating internal surfaces. The sum of all these heat sources is know as the heat gain (or heat load) of the building, and is expressed either in BTU (British Thermal Units) or Kw (Kilowatts). For an air conditioner to cool a room or building its output must be greater than the heat gain. It is important before purchasing an air conditioner that a heat load calculation is performed to ensure it is big enough for the intended application. Heat load calculations There are several different methods of calculating the heat load for a given area: Quick calculation for offices For offices with average insulation and lighting, 2/3 occupants and 3/4 personal computers and a photocopier, the following calculations will suffice: Heat load (BTU) = Length (ft.) x Width (ft.) x Height (ft.) x 4 Heat load (BTU) = Length (m) x Width (m) x Height (m) x 141 For every additional occupant add 500 BTU. If there are any additional significant sources of heat, for instance floor to ceiling south facing windows, or equipment that produces lots of heat, the above method will underestimate the heat load. In which case the following method should be used instead. A more accurate heat load calculation for any type of room or building The heat gain of a room or building depends on: The size of the area being cooled The size and position of windows, and whether they have shading The number of occupants Heat generated by equipment and machinery Heat generated by lighting By calculating the heat gain from each individual item and adding them together, an accurate heat load figure can be determined. Step One Calculate the area in square feet of the space to be cooled, and multiply by 31.25 Area BTU = length (ft.) x width (ft.) x 31.25 Step Two Calculate the heat gain through the windows. If the windows don’t have shading multiply the result by 1.4 North window BTU = Area of North facing windows (m. sq.) x 164 If no shading, North window BTU = North window BTU x 1.4 South window BTU = Area of South facing windows (m. sq.) x 868 If no shading, South window BTU = South window BTU x 1.4 Add the results together. Total window BTU = North window + South window Step Three Calculate the heat generated by occupants, allow 600 BTU per person. Occupant BTU = number of people x 600 Step Four Calculate the heat generated by each item of machinery - copiers, computers, ovens etc. Find the power in watts for each item, add them together and multiply by 3.4 Equipment BTU = total equipment watts x 3.4 Step Five Calculate the heat generated by lighting. Find the total wattage for all lighting and multiply by 4.25 Lighting BTU = total lighting watts x 4.25 Step Six Add the above together to find the total heat load. Total heat load BTU = Area BTU + Total Window BTU + Occupant BTU + Equipment BTU + Lighting BTU Step Seven Divide the heat load by the cooling capacity of the air conditioning unit in BTU, to determine how many air conditioners are needed. Number of a/c units required = Total heat load BTU / Cooling capacity BTU

VRF&VRV

VRV or VRF ? What’s the difference between VRV and VRF? Many people who ask this question, mistakenly interpret it as 2 different HVAC technologies. Actually, those are two different terms for the same type of HVAC technology. Based on Inverter technology compressors, the first VRV HVAC systems were invented by Daikin during the early 1980’s. As a technology leader in the HVAC industry, Daikin had registered the VRV term (which stands for Variable Refrigerant Volume1) as an official trademark. All other companies use VRF (Variable Refrigerant Flow2) for their similar HVAC systems. Eventually, VRF is the more common term for these types of systems, and this is the term that will be used for the rest of the article. Wish to integrate your VRF to Home Automation system? Check out our simple solutions. So what is VRF? It can easily be related to as the “Rolls Royce” of Air Conditioning Systems. It’s a very sophisticated technological air conditioning system, based on several principles: Refrigerant only – where refrigerant is the only coolant material in the system (in contrary to the chilled water systems, where refrigerant is used for cooling/heating the water that is circulated throughout the whole system). Inverter compressors that allow lowering power consumption with partial cooling/heating loads. Several air handlers (indoor units) on the same refrigerant loop / circuit. Ability of modular expansion (especially applicable for large projects, that can grow in stages). Typical VRF system structure A typical system consists of an outdoor unit (comprising one or multiple compressors), several indoor units (often and mistakenly called “fan coils”), refrigerant piping, running from the outdoor to all indoors, using Refnet Joints (copper distributors in pipes) and communication wiring. VRV / VRF HVAC connectivity diagam Communication wiring consists of a 2 wired cable, chained from the outdoor to all indoors, creating an internal closed loop network, that is an essential part of any VRF installation. As for the Control, each indoor is controlled by its own wired control panel, while there are some possibilities for wireless remotes (IR) and centralized controllers, enabling controlling all indoors from one location. How does VRF HVAC work? The operation logic of the VRF is fully built-in inside the system and is proprietary for each VRF manufacturer. The system gets inputs from the user (e.g. desired comfort temperature) and from the surroundings (outside ambient temperature), and according to that data it implements its logic in order to get to the desired comfort conditions, utilizing optimal power consumptions. The ability to adjust itself to the outdoor conditions is one of the main factors that makes these systems so efficient, compared to the traditional water cooled systems, based on chillers and fan coils. Now, let’s dive in, and see how it works in details. Let’s take as an example a typical VRF installation, with one outdoor unit and multiple indoors. At the beginning, the system is in standstill condition (everything is turned off). Once a user turns one of the indoors “ON” by its local remote, the outdoor “gets noted” regarding it, and starts working. At this point, it will examine the outdoor conditions (temperature), the operating indoor requirements (operation mode, set point temperature), and will operate the compressor at the exact level, required to comply with the indoor requirements. When another indoor unit is turned on, the outdoor recalculates the requirements from all the indoors, and will increase the compressor’s output, according to the required level of demand. This process is constantly occurring with any change, performed in the HVAC system. As described, this system is fully automatic, and regulates its power consumption based on the demand arriving from the indoor units and outside prevailing conditions. User can have influence on the desired indoor comfort conditions, modifying: Operation mode (on/off), Operation state (Cool/Heat/Fan/Dry/Auto), setpoint temperature, fan speed (high/medium/low/auto). Controlling those parameters is the only thing required for proper operation, and the only thing that is required for proper integration with the VRF system. VRF System types Cooling only systems (less popular) – those systems can only cool. Heating is not available. Fan and Dry modes are available for each indoor unit independently. Heat Pump systems (most popular) – all the indoor units can either heat, or cool (not at the same time). Fan and Dry modes are available for each indoor unit independently. Heat Recovery systems (less popular) – those systems are the most sophisticated ones, where cooling and heating may be available by each indoor unit, independently, at the same time.