Delta tThe effectof temperaturedifference onlow temperaturesystems(difference in heat emitter and desired room)Correction factor table1.267605550454035302520151051.13210.8720.7480.6260.5150.406Effect on heat emitter output0.3040.2090.1230.0500.20.40.60.811.21.4Limitations in the use of correction factors for low temperature systems.It is true that the above correction factors apply when considering the relative sizes of a heatemitter (panel radiator) when applied (in similar circumstances) to systems operating atvarying temperature differences (Delta t).However, it is a comparator only. To ensure that the heat emitters provide the correct comfortlevels and work in a way that is consistent with both the building and the heat pump it isimportant that the heat transferred to the environment (heat loss) is properly calculated. Boththe heat generator (heat pump) and the emitters (radiators) are selected with a suitable outputin accordance these calculations (heat losses).Comparison of radiator size and outputs at Delta t 50 and Delta t 40The following examples demonstrate how the size and surface area of a radiator need to increaseto achieve the desired output (BTU) of a radiator at Delta t 40 compared to a Delta t 50 outputthat is achieved by a traditional boiler.The correct output of a radiator at a lower Delta t (20 or 30) can be calculated by contacting anMCS accredited installer, who will work out the correct size of radiator to suit your space.As the Delta t ( temperature difference) can be half that of a boilerwhen the flow temperatures of a heat pump are considered thenmore than twice as much emitter (heat exchanger) surface area isrequired. The heat emitter needs to be physically larger.Example 1RADIATOR AT DELTA T 50Adjustment factors for a range of temperature differencesbetween the emitter (in this case a panel radiator) andair in the living space (Delta t) is shown below.HeightLengthTypeBTU600400K22,365Example 2RADIATOR AT DELTA T 40Height LengthRADIATOR AT DELTA T 50RADIATOR AT DELTA T 40TypeBTUHeightLengthTypeBTUHeightLengthTypeBTUK22,652600800K24,7306001100K24.8635,006600600700600K23,0057001100K2700600P+2,3447001400K25,4683001000K33,443700700K34,8441600300K22,7801800500K25,053At Delta t 40 the the surface area of the radiator needs to be larger. The surface area is determinedby height, width and the depth of the radiator. Here are a couple of examples.Example 1DELTA T 50BTU : 2365DELTA T 40BTU : 2652DELTA T 50BTU : 4,730H: 600Type K3>>>W: 600H: 1800H: 700>>>16DELTA T 40BTU : 4,844Type K2Type K2H: 600W: 400Type K2Example 2Type K2H: 600DELTA T 40BTU : 5,053W: 800>>>W: 700W: 50017
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