METHOD FOR OPERATING A HEAT PUMP SYSTEM, HEAT PUMP SYSTEM AND HVAC SYSTEM

Abstract

The invention relates to a method for operating a heat pump system, a heat pump system and an HVAC system measuring a solar irradiance, wherein the operation of the heat pump is adjusted based on the solar irradiance.

Claims

1. Method for operating a heat pump system, comprising measuring a solar irradiance incident onto a building, and adjusting an operation of a heat pump included in the heat pump system based on the measured solar irradiance.

2. Method according to claim 1, wherein the operation of the heat pump is adjusted only when the solar irradiation is larger than a predetermined threshold.

3. Method according to claim 1, wherein the operation of the heat pump is adjusted using feed forward control and/or feedback control, the method further comprising using the measured solar irradiation to adjust, preferably to reduce, at least one of the following quantities entering the feed forward control and/or the feedback control by a temperature correction amount: a target flow temperature of the heat pump, a flow temperature set-point and/or an air temperature set point of an indoor air temperature.

4. Method according to claim 3, wherein in the adjusting of the operation of the at least one heat pump the temperature correction amount is determined from the measured solar irradiation using a solar heat gain coefficient, SHGC, method, a Overall Solar Aperture Coefficient Method and/or a Standard Assessment Procedure, SAP.

5. Method according to claim 1, wherein the operating frequency of a compressor included in the heat pump is adjusted to adjust the operation of the heat pump.

6. Method according to claim 1, wherein the operation of the heat pump is adjusted using feed forward control and/or feedback control, wherein the method further comprises comparing the measured solar irradiance to a threshold irradiance, if the measured solar irradiance is equal or larger than the threshold irradiance then determining a solar gain as Q.sub.solar=, wherein is a solar aperture coefficient, determining a flow temperature reduction as T=Q.sub.solar/(m C.sub.p), wherein m is a mass flow rate of a heat transfer fluid of the heat pump system and C.sub.p is a specific heat capacity of the heat transfer medium of the heat pump system and adjusting the operation of the heat pump by reducing a target flow temperature T.sub.flow,supply of the heat pump by T.

7. Method according to claim 1, wherein the operation of the heat pump is adjusted using feed forward control and/or feedback control, wherein the method further comprises comparing the measured solar irradiance to a threshold irradiance, if the measured solar irradiance is equal or larger than the threshold irradiance then determining a solar gain as Q.sub.solar=, wherein is a solar aperture coefficient, determining an air temperature reduction as T=Q.sub.solar/M, wherein M is a thermal mass of the building and adjusting the operation of the heat pump by reducing the indoor temperature set point T.sub.indoor sp by T.

8. Method according to claim 1, wherein the solar irradiation is measured by a sensor located on the outside of the building, preferably at a highest point of the building or at a spot of the building having unobstructed view of the sun during the whole day.

9. Method according to claim 1, wherein the steps of the method are carried out at least once every hour, preferably at least once every 15 minutes, preferably at least once every minute.

10. Heat pump system, comprising at least one heat pump, at least one sensor configured for measuring a solar irradiance onto a building, a controller configured for controlling an operation of the at least one heat pump based on an amount of solar irradiance measured by the at least one solar irradiance sensor for measuring a solar irradiance.

11. Heat pump system according to claim 10, wherein the controller is configured to adjust an operating frequency of a compressor included in the at least one heat pump as the operation of the at least one heat pump based on the solar irradiation.

12. Heat pump system according to claim 10, wherein the solar irradiance sensor is a silicon photo cell or a thermopile type sensor.

13. Heat pump system according to claim 10 wherein the heat pump is configured to carry out a method according to claim 1.

14. HVAC system including a heat pump system according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In the following the disclosure will be described by way of examples with reference to figures. The features described in the context of the examples can also be realized independently from the specific example.

[0028] FIG. 1 shows a functional diagram of an auto-tuning-feed-forward control and feed-back control of the prior art,

[0029] FIG. 2 shows the effect of the present disclosure,

[0030] FIG. 3 shows a control diagram of a heat pump operating method in which the target flow temperature is adjusted,

[0031] FIG. 4 shows a control algorithm for the flow temperature set point adjustment in FIG. 3,

[0032] FIG. 5 shows a control diagram of a heat pump operation in which the indoor temperature set point is adjusted, and

[0033] FIG. 6 shows a control algorithm of the indoor temperature set point adjustment in FIG. 5.

DESCRIPTION OF EMBODIMENTS

[0034] Calculating solar heat gain is a process that involves details about window size, orientation, shading, and material properties along with estimates of direct and indirect solar irradiance. Solar gain can be expressed by the Equations (1)-(6) [ASHRAE Research, ASHRAE HandbookFundamentals; Atlanta: ASHRAE 2017].

[00001]$\begin{array}{cc}.Math.q_s=E_{D.Math.N}.Math.\cos \left(\right).Math.\left(T-N.Math.A\right).Math.W_A& \left(1\right)\\ .Math.\mathrm{SHGC}\left(,\right)=T\left(,\right)-\mathrm{NA}\left(,\right)& \left(2\right)\\ .Math.q_s=E_{D.Math.N}.Math.\cos \left(\right).Math.\mathrm{SHGC}\left(,\right).Math.W_A& \left(3\right)\\ .Math.\mathrm{SHGC}\left(\right)=T\left(\right)-\underset{k=1}{\overset{L}{.Math.}}.Math.N_k.Math.A_k& \left(4\right)\\ .Math.q_s=I{\mathrm{SHGC}}_e\left(\right){\mathrm{AR}}_e& \left(5\right)\\ \cos \left(\right)=\sin \left(\right).Math.\sin \left(\right).Math.\cos \left(\right)-\sin \left(\right).Math.\cos \left(\right).Math.\sin \left(\right)-\cos \left(\right).Math.\cos \left(\right).Math.\cos \left(\right).Math.\cos \left(\right)-\cos \left(\right).Math.\sin \left(\right).Math.\sin \left(\right).Math.\cos \left(\right).Math.\cos \left(\right)-\cos \left(\right).Math.\sin \left(\right).Math.\sin \left(\right).Math.\sin \left(\right)& \left(6\right)\end{array}$

[0035] Since total solar readings were recorded normally and also in various data sources, it is necessary to split the total radiation into direct and diffuse components [2].

I/I.sub.0=1.00.09k.sub.T, for k.sub.T0.22(7)

I/I.sub.0=0.95110.1604k.sub.T+4.388k.sub.T.sup.216.638k.sub.T.sup.3+12.366k.sub.T.sup.4, for 0.22<k.sub.T0.8(8)

I/I.sub.0=0.165, k.sub.T>0.8(9)

[0036] In an advantageous embodiment the solar heat gain introduced into a building can be determined from the measured solar irradiance using a solar feed gain coefficient, SHGC, method.

[0037] Data that actually provided by a manufacturer of windows typically include: [0038] Number of layerssingle pane, double or triple pane? [0039] Description of the glass typecoloration, whether or not it has low E coating [0040] U-factor (NFRC2004b) [0041] Solar Heat Gain Coefficient(SHGC) at normal incident angle [0042] Visual transmittance

[0043] Preferably, conduction heat gain is computed separately from the transmitted and absorbed solar heat gain. Because the thermal mass of glass is normally very low, the conduction is approximately steady state. Accordingly, the conduction heat gain may be calculated as:

q.sub.cond=UA(T.sub.outdoorT.sub.indoor)(10)

[0044] Transmitted and absorbed solar heat gains are advantageously calculated as follows:

1. Compute the incidence angle, surface azimuth angle, incident direct irradiation and diffuse irradiation on windows;
2. If exterior shading exists, determine sunlit area and shaded area;
3. For windows without shading, the beam and diffuse and total heat gain are given:

q.sub.SHG,Direct=E.sub.DirectA.sub.unshadedSHGC()(11)

q.sub.SHG,Diffuse=(E.sub.Diffuse+E.sub.reflected)A.sub.totalSHGC.sub.diffuse(12)

q.sub.SHG,=q.sub.SHG,Direct+q.sub.SHG,Diffuse(13)

where
SHGC() is the angle dependent SHGC interpolated as in Table 1.

TABLE-US-00001 TABLE 1 Window optical properties and SHGC Hemi- Angle 0 10 20 30 40 50 60 70 80 90 spherical Single pane, 3 mm thick, clear .sub.sol 0.834 0.833 0.831 0.827 0.818 0.797 0.749 0.637 0.389 0 0.753 .sub.1 0.091 0.092 0.094 0.096 0.100 0.104 0.108 0.110 0.105 0 0.101 SHGC 0.859 0.859 0.857 0.854 0.845 0.825 0.779 0.667 0.418 0 0.781 Double pane, both panes 3.2 mm thick with low e coating, inner pane 5.7 mm thick .sub.sol 0.408 0.410 0.404 0.395 0.383 0.362 0.316 0.230 0.106 0 0.338 .sub.1 0.177 0.180 0.188 0.193 0.195 0.201 0.218 0.239 0.210 0 0.201 .sub.2 0.06 0.060 0.061 0.061 0.063 0.063 0.061 0.053 0.038 0 0.059 SHGC 0.469 0.472 0.466 0.459 0.448 0.428 0.382 0.291 0.152 0 0.400 Double pane, both panes 5.7 mm thick, clear .sub.sol 0.607 0.606 0.601 0.593 0.577 0.546 0.483 0.362 0.165 0 0.510 .sub.1 0.167 0.168 0.170 0.175 0.182 0.190 0.200 0.209 0.202 0 0.185 .sub.2 0.113 0.113 0.115 0.116 0.118 0.119 0.115 0.101 0.067 0 0.111 SHGC 0.701 0.701 0.698 0.691 0.678 0.648 0.585 0.456 0.237 0 0.606 Note: Data generated with the WINDOW program [4].

[0045] Another advantageous method for calculating the solar heat gain is for example the overall solar aperture coefficient method.

[0046] This method is for example used in co-heating tests which involve the creation of a further whole building parameter, the solar aperture, (A.sub.sol (m.sup.2)), defined by its use within the regression process and the measurement of incident solar radiation. The term A.sub.sol is well defined by P. Baker, A retrofit of a Victorian terrace house in New Bolsover: a whole house thermal performance assessment, Historic England & Glasgow Caledonian University, 2015, which refers to the solar aperture as the heat flow rate transmitted through the building envelope to the internal environment under steady state conditions, caused by solar radiation incident at the outside surface, divided by the intensity of incident solar radiation in the plane of the building. It can be regarded as equivalent to a totally transparent area which lets in the same solar energy as the whole building.

[0047] As the total heat flow across the building fabric cannot be measured directly, the co-heating method uses a simplified energy balance equation to infer heat loss as shown equation (14) in an unoccupied house.

[00002]$\begin{array}{cc}{Q}_{\mathrm{active}}+Q_{\mathrm{sol}}=Q_{\mathrm{loss}}& \left(14\right)\\ Q_{\mathrm{active}}+A_{\mathrm{sol}}.Math.I_{\mathrm{sol}}=\mathrm{HLC}.Math.\left(T_{\mathrm{indoor}}-T_{\mathrm{outdoor}}\right)& \left(15\right)\\ Q_{\mathrm{active}}=\mathrm{HLC}.Math.\left(T_{\mathrm{indoor}}-T_{\mathrm{outdoor}}\right)-A_{\mathrm{sol}}.Math.I_{\mathrm{sol}}& \left(16\right)\\ \frac{Q_{\mathrm{active}}}{T_{\mathrm{indoor}}-T_{\mathrm{outdoor}}}=-A_{\mathrm{sol}}.Math.\frac{I_{\mathrm{sol}}}{T_{\mathrm{indoor}}-T_{\mathrm{outdoor}}}+\mathrm{HLC}& \left(17\right)\end{array}$

Q.sub.active is the heat supplied either by electric or heat pump, W.
HLC is the heat loss coefficient, W/K.
Based on measured parameters and the HLC and A.sub.sol can be obtained in a long period of tests.

[0048] The value of A.sub.sol is a function of not only glazing characteristics of the dwelling but also its thermal mass.

[0049] A further advantageous method for determining the solar heat gain is the standard assessment procedure, SAP.

[0050] As described in BRE, The Government's Standard Assessment Procedure for Energy Rating of Dwellings (SAP 2012), Garston: BRE, 2017. Solar gains are calculated using solar flux from U3 in Appendix U and associated equations to convert to the applicable orientation.

G.sub.solar=0.9A.sub.wSg.sub.FFZ

Where

[0051] G.sub.solar is the average solar gain, W;
0.9 is the factor repenting the ratio of typical average transmittance to that at normal incidence;
A.sub.w is the area of an opening (a window or a glazed door), m2;
S is the solar flux on the applicable surface, W/m2;
g.sub. is the total solar energy transmittance factor of the glazing at normal incidence
FF is the frame factor for windows and doors (fraction of opening that is glazed);
Z is the solar access factor.
The factors can be estimated in Tables 2, 3 and 4.

TABLE-US-00002 TABLE 2 Transmittance factors for glazing Total Light Glazing solar energy transmittance, Type transmittance, g.sub. g.sub.L Single glazed 0.85 0.9 Double glazed (air or argon filled) 0.76 Double glazed (low-E, hard-coat) 0.72 Double glazed (low-E, soft-coat) 0.63 {close oversize brace} 0.8 Window with secondary glazing 0.76 Double glazed (air or argon filled) 0.68 Double glazed (low-E, hard-coat) 0.64 {close oversize brace} 0.7 Double glazed (low-E, soft-coat) 0.53

TABLE-US-00003 TABLE 3 Frame factors Frame Type Frame Factor Wood 0.7 Metal 0.8 Metal, thermal break 0.8 PVC-U 0.7

[0052] Note: if know the actual frame factor should be used instead of the data in the Table.

TABLE-US-00004 TABLE 4 Solar and light access factors % of sky blocked Winder solar Summer solar Light access Overshading by obstacles access factor* access factor** factor Heavy >80% 0.3 0.5 0.5 More than >60%-80% 0.54 0.7 0.67 average Average or 20%-60% 0.77 0.9 0.83 unknown Very little <20% 1.0 1.0 1.0 Note: *for calculation of solar gains for heating. **for calculation of solar gains for cooling and summer temperatures.

[0053] FIG. 2 shows the effect of the present disclosure. FIG. 2(a) shows the air temperature and the solar irradiance throughout the day in the upper diagram and the compressor frequency and the heat pump power throughout the day in the lower diagram for a prior art heat pump control. FIG. 2(b) shows the air temperature and solar irradiance over the course of the day in the upper diagram and the compressor frequency and heat pump power over the day in the lower diagram for a heat pump system controlled according to the present disclosure.

[0054] In the upper diagrams of FIGS. 2(a) and 2(b) the full line indicates the solar irradiance, the short dashed line indicates the ambient temperature and the long dashed line indicates the set point indoor temperature. In the lower diagrams of FIGS. 2(a) and 2(b) the thick full lines indicate the heat pump power and the thin full lines indicate the compressor frequency.

[0055] The solar irradiance starts increasing with sunrise, reaches its maximum at noon and reaches zero at sunset.

[0056] As in the prior art the heat pump is controlled based on the measured indoor temperature, the compressor frequency in FIG. 2(a) is reduced at a time t.sub.0 where the indoor temperature starts to increase. At a time t.sub.1 the compressor is fully shut down if the indoor temperature reaches a certain value. The heat pump power follows the compressor frequency in the lower diagram of FIG. 2(a).

[0057] In FIG. 2(b) showing the effect of the disclosure the heat pump operation is controlled based on the measured solar irradiance. If at a time t.sub.0 the solar irradiance increases above a threshold irradiance the compressor frequency f is reduced and at the same time the heat pump power is reduced. If at a time t.sub.1 the solar irradiance increases above a further threshold the compressor frequency f is set to zero and correspondingly the heat pump power becomes zero. It can be seen in the upper diagram of FIG. 2(b) that the indoor temperature, represented by the full line, stays closer to the set point temperature indicated by the long dashed line than in the conventional control shown in the upper diagram of FIG. 2(a). Furthermore, it can be seen that the compressor frequency is reduced at the earlier times to and t.sub.1 than the times t.sub.0 and t.sub.1 in the conventional control method. Therefore, energy of the heat pump operation is saved as indicated by the hashed regions in the lower diagram of FIG. 2(b).

[0058] FIG. 3 shows a control diagram of a method for operating a heat pump system according to the disclosure. The method employs a feed-forward control 1 as well as a feed-back control 2. On the left side a set room temperature enters firstly an optional low pass filter 6 and then enters the feed-forward control 1 where together with a measured ambient temperature a target flow temperature is calculated. The output of the low pass filter 6 is furthermore input into the feed-back control element 2 which also produces a target flow temperature. The target flow temperature provided by the feed-forward control 1 and the feed-back control 2 are combined to a resulting target flow temperature. This resulting target flow temperature is in this embodiment adjusted in step 8 based on a solar irradiance measured by a suitable solar irradiance sensor. Step 8 outputs an adjusted target flow temperature. This adjusted target flow temperature goes through the power safe control 3, the outdoor unit 4 and the house 5 to result in a room temperature. The room temperature is fed back via the low pass filter 7 to the input of the feed-back control so that the difference between the set room temperature output by the low pass filter 6 and the fed back room temperature output by the low pass filter 7 is input into the feed-back control 2.

[0059] The Power save control 3 is a function to reduce the compressor frequency fluctuation, in order to smoothen the operation and thus save power consumption due to sudden change of compressor frequency. Outdoor unit 4 is the block of a heat pump outdoor unit with the main refrigeration cycle, which operates in outdoor environment to absorb the low grade energy from the ambient such as air or ground. House 5 is a block representing the building which requires heat supplied from heat pump for maintaining a certain temperature.

[0060] FIG. 4 shows a flow diagram of an algorithm carried out in the control diagram of FIG. 3. In a first step S1 an indoor temperature in a room heated by the heat pump is measured. Furthermore, in a step S2 an ambient temperature is measured, which is for example an outdoor temperature. It should be noted that although steps S1 and S2 are shown in a certain sequence in FIG. 4, they can be carried out in different order and also at the same time.

[0061] In step S3 an initial temperature T.sub.flow,supply is calculated. This initial T.sub.flow,supply is provided from the input value from the previous block indicated as target flow temperature in FIG. 3. This value is initially calculated from the feed-forward control block 1 and the feed-back control block 2 in FIG. 3.

[0062] In a step S4 a solar flux is acquired, for example by a sensor or by other web based data. A dimension of the solar flux is for example W/m.sup.2. It should be noted that in FIG. 4 step S4 is shown after step S3. However, the solar flux could as well be acquired at any other point of the sequence of steps S1, S2 and S3.

[0063] The following steps S5, S6, S7, S8 and S9 are carried out in block 8 in FIG. 3.

[0064] In step S5 it is decided whether the acquired solar flux is greater than a threshold irradiation, for example .sub.threshold=50 W/m.sup.2. If this is not the case, the target flow temperature T.sub.flow,supply is not modified. If, on the other hand, the measured solar flux is greater than the threshold flux .sub.threshold, step S6 is carried out, where a solar gain Q.sub.solar is estimated as Q.sub.solar=. In this example, the solar gain Q.sub.solar [W] absorbed in the building is estimated. Here, the solar aperture coefficient [m.sup.2] and the coefficient can be derived, for example, by a regression method in co-heating tests or continuous heating tests of a certain duration.

[0065] The estimated solar gain Q.sub.solar is then used in step S7 to estimate a flow temperature reduction T as T=Q.sub.solar/(mC.sub.p). Using this value in step S8, the target flow temperature T.sub.flow,supply is adjusted by subtracting the flow temperature reduction T, that is, T.sub.flow,supply:=T.sub.flow,supplyT. In step S9, the target flow temperature is then updated and can be used for the control of the heat pump.

[0066] In step S7, the temperature adjustment is calculated based on the solar gain Q.sub.solar divided by the mass flow rate of the fluid m [kg/s], and the specific heat capacity of the fluid C.sub.p [J/(kgK)], such as glycol water.

[0067] In step S8, the new flow temperature supplied to the building by the heat pump is reduced by T.

[0068] FIG. 5 shows a control diagram of a method for operating a heat pump according to a further embodiment of the disclosure. FIG. 5 corresponds to FIG. 3, but does not have the block 8 in which the target flow temperature is adjusted in FIG. 3, but instead has an additional block 9 where an indoor temperature set point is adjusted based on acquired solar irradiance. Regarding blocks 1 to 7, reference is made to FIG. 3.

[0069] A set temperature is input into the control, and this set temperature is then adjusted in block 9 before being input into the low pass filter 6.

[0070] An algorithm carried out in block 9 is shown in FIG. 6. Again, in steps S1, S2, and S4 an indoor temperature in a room to be heated by the heat pump is measured, an ambient temperature, for example an outdoor temperature, is measured, and a solar flux is acquired. Steps S1, S2, S4 can be carried out in any order and also at the same time. Again, the solar irradiance [W/m.sup.2] can, for example, be acquired by an installed sensor or by web-based data.

[0071] In step S5 the acquired solar flux is then compared to a threshold .sub.threshold, for example .sub.threshold=50 W/m.sup.2, in order to judge whether the solar irradiance is sufficiently significant.

[0072] If that is the case, in step 6 the solar gain Q.sub.solar is estimated as Q.sub.solar=. In this embodiment, as also in the other embodiments, for example be derived from TAITherm simulation results.

[0073] The estimated solar gain Q.sub.solar is then used in step S10 to estimate the indoor temperature reduction T as T=Q.sub.solar/M, wherein M [W/K] is the thermal mass of the building, for example according to SAP or some other standard.

[0074] Using this temperature reduction T, the indoor temperature set point T.sub.indoor,sp is then reduced as T.sub.indoor,sp:=T.sub.indoor,spT. The corrected value is then updated in step S9 to be used for the further control of the heat pump as shown in FIG. 5, starting in block 6.

[0075] In the case where the heat pump heats the indoor space as well as in the case where the heat pump or air conditioner cools the indoor space, the adjustment of the temperatures will usually be a reduction of these temperatures because the solar radiation adds additional heat into the indoor space.

[0076] The utilization of solar gain according to the present disclosure allows saving energy, as it takes a long time for heat pump controllers according to the prior art to recognize that there is a significant amount of solar gain, as the prior art controllers only measure the indoor temperature. The solar gain is mainly stored in the thermal mass when it arrives in the living space.

[0077] The present disclosure is capable of avoiding overheating, which usually is a problem in conventional heating systems due to the limitation of feedback control and the nature of solar gain to the house. The disclosure can minimize overheating.

[0078] A heat pump such as employed in the present disclosure can, for example, be an air-to-water (A2W) heat pump or a ground source heat pump (GSHP) or any heat pump incorporating a refrigerant circuit.