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HeatPump

Air-to-water heat pump (Buildings ModularReversible AirToWaterTableData2D, Vitocal 251-A08 scaled to its capacity) charging a mixed buffer; with set flows, the reference of its circuit (no mass balance)

FastSmoothBuildings.Hydronics.HeatPump, model (source)

Extends PartialFlow.

Purpose

Air-to-water heat pump at the compressor speed y, its performance from the table of the Viessmann Vitocal 251-A08 (HeatPumps.Vitocal251A08) scaled to Q_flow_nominal. It charges a mixed buffer at the temperature T, a storage tank or a hydraulic separator, from which the heating circuit draws at T. The source is the outdoor air of the weather bus.

Equations

With Qtab and Ptab the heating capacity and electrical power of the table, as smoothTable gives them at the condenser outlet temperature and the outdoor dry-bulb temperature Tsou:

Tcon,out = T + dTCon y,

Qcon = y s Qtab(Tcon,out, Tsou),   Pele = y s Ptab(Tcon,out, Tsou),   COP = Qtab/Ptab,

C dT/dt = mTra cp (TIn − T) + Qcon + UA (TAmb − T).

Both Qcon and Pele scale with y, so the COP is defined at every speed, also with the compressor off. The electricity meter EEle integrates Pele in kWh.

Parameters

  • scaFac (s): Q_flow_nominal over the capacity of the table at the supply temperature TSet and the outdoor temperature TOutDes, by the linear interpolation of interpolate.
  • mCon_flow: the condenser flow of the record scaled by scaFac; dTCon = Q_flow_nominal/(cp mCon_flow), the rise of the condenser outlet above the buffer at full speed.
  • useStorageTank: with a tank, the water volume is VTan and the heat loss conductance that of a cylinder of volume VTan and height hTan (side and both ends) insulated by dIns of conductivity kIns; without, a hydraulic separator without loss, of 1.5·10−5 m3 per W of Q_flow_nominal.
  • C: heat capacity of the buffer water and of the water in the condenser, taken as mCon_flow tauCon.
  • dTSou: width over which the kinks of the table in the source temperature are smoothed.

Set flows and pressure-driven flows

With set flows, the heat pump is the reference of its circuit: it has no mass balance, the circuit closes it. With pressure-driven flows, its outlets have the small linear conductance m_flow_nominal/dpLink, shared evenly by the outlet connections; the heating side of Buildings has no resistance.

Relation to Buildings

Buildings.Fluid.HeatPumps.ModularReversible.AirToWaterTableData2D with the Vitocal 251-A08 data, scaled to its capacity.

Use

Examples.HeatPumpCircuit: a buffer and two radiators in closed loop.

Parameters

Parameter Type Unit Default Description
m_flow_nominal Real kg/s Q_flow_nominal/cpWat/5 Nominal flow of the heating circuit
dpLink Real Pa 100 Pressure drop at the nominal flow (pressure-driven flows; the heating side of Buildings has none)
GLink Real kg/(s.Pa) m_flow_nominal/dpLink
Q_flow_nominal Real W Heating capacity at the design outdoor and supply temperatures
TSet Real K 318.15 Supply temperature at design conditions
TOutDes Real K 265.15 Design outdoor temperature
useStorageTank Boolean false Buffer tank; a hydraulic separator otherwise
VTan Real m3 0.1 Volume of the buffer tank
hTan Real m 0.8 Height of the buffer tank
dIns Real m 0.1 Insulation thickness of the buffer tank
kIns Real W/(m.K) 0.04 Insulation conductivity
TAmb Real K 288.15 Temperature around the buffer
tauCon Real s 30 Time constant of the condenser
dTSou Real K 1 Smoothing of the table interpolation in the source temperature
scaFac Real Q_flow_nominal/HeatPumps.Vitocal251A08.interpolate(TSet, TOutDes, true) Scaling of the table data to the capacity
mCon_flow Real kg/s HeatPumps.Vitocal251A08.mCon_flow_nominal*scaFac Condenser flow
dTCon Real K Q_flow_nominal/cpWat/mCon_flow Condenser outlet above the buffer at full speed
VWat Real m3 if useStorageTank then VTan else 1.5e-5*Q_flow_nominal Water volume
UA Real W/K if useStorageTank then kIns/dIns(2pisqrt(VTan/(pihTan))hTan + 2piVTan/(pihTan)) else 0 Heat loss conductance of the buffer
C Real J/K (rhoWatVWat + mCon_flowtauCon)*cpWat Heat capacity of the buffer and condenser
T_start Real K TSet Initial buffer temperature

Revisions

  • October 2026: moved from trano's FastModel.Hydronics.