Electric power demand limit for variable speed heat pumps and integrated water heating heat pumps

• US 5,095,715 A
• Filed: 09/20/1990
• Issued: 03/17/1992
• Est. Priority Date: 09/20/1990
• Status: Expired due to Fees

• Current Assignee: Electric Power Research Institute Incorporated
• Original Assignee: Electric Power Research Institute Incorporated
• Inventors: Dudley, Kevin F.
• Primary Examiner(s): BENNETT, HENRY A
• Application Number:
  US07/585,385
• Time in Patent Office: 544 Days
• Field of Search: 237/2 B, 62/230, 62/231, 62/228.1, 62/228.4, 307/35, 307/30, 307/36, 307/37, 307/38, 307/39
• US Class Current: 62/228.4
• CPC Class Codes: F24D 17/02 using heat pumps
• CPC Class Codes: F24F 5/0096 combined with domestic apparatus
• CPC Class Codes: F25B 2600/0253 with variable speed
• CPC Class Codes: F25B 49/02 for compression type machines, plants or systems
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

An integrated heat pump and hot water system provides heating or cooling of a comfort zone, as required, and also provides water heating. As a power management feature, the speed of a variable speed compressor is reduced to a predetermined fraction, e.g. 80%, of its normal operating speed, in response to a demand limit signal provided from the electric power utility during times of peak electrical load. A reference compressor speed is computed based on the current compressor speed, indoor temperature, outdoor temperature, and zero-load temperature difference. If the system is between operating cycles when the demand limit signal is received, a stored speed is used which corresponds to the compressor speed at a predetermined outdoor-indoor temperature difference. This system produces graceful reduction in comfort cooling during demand limit periods.

Claims

1. Method of operating an integrated heat pump and hot water system that is capable of providing heating or cooling to an environmental comfort zone, said heat pump and hot water system including a variable speed compressor whose operating speed is substantially linearly related to the difference between outdoor air temperature and indoor air temperature in the comfort zone, and also including means to receive a utility peak demand limit signal to initiate automatic power limiting to reduce the power demand imposed by the heat pump and hot water system, the method comprising sensing the outdoor temperature T_OD ;

sensing the indoor temperature T_ID in the comfort zone;

sensing the speed S₁ of the variable speed compressor; and

in response to receiving said utility peak demand limit signal DLS calculating a reference speed S_R for the compressor as a function of said speed S₁, said outdoor temperature T_OD, said indoor temperature T_ID, and predetermined values that correspond to a reference indoor temperature T_ID and a zero-load temperature difference Δ

T_Z that corresponds to the difference between the outdoor and indoor temperatures that result in a zero load requirement on said compressor; and

during occurrence of said signal DLS operating the compressor at a reduced operating speed limited to a predetermined fraction, less than unity, times said reference speed S_R.

2. Method of operating a heat pump and hot water system according to claim 1 wherein said reference speed S_R is calculated according to the relationship:

##EQU7## .

3. Method of operating a heat pump and hot water system according to claim 2, wherein said zero-load temperature difference Δ

T_Z is on the order of -13 degrees F. (-7.2°

C.).

4. Method of operating a heat pump and hot water system according to claim 1 wherein the system also comprises a water heater having a heat pump water exchanger following said compressor and an auxiliary resistive water heating element, the method further comprising disabling said auxiliary resistive water heating element in response to said utility peak demand limit signal.

5. Method of operating a heat pump and hot water system according to claim 1 further comprising storing an operating speed S_P representing the compressor speed at a time during a cycle when the compressor had most recently run for use when said utility peak demand limit signal is received while the compressor is not running;

storing a reference temperature difference Δ

T_R representing the difference between the indoor temperature and the outdoor temperature at a time during the cycle when the compressor had most recently run, and computing said reference speed S_R based on the stored operating speed S_P, the reference temperature difference Δ

T_R, said indoor temperature T_ID, said outdoor temperature T_OD, and said zero-load temperature difference Δ

T_Z.

6. Method of operating a heat pump and hot water system according to claim 5 wherein said reference speed S_R is calculated according to the relationship:

##EQU8## .

7. Method of operating a heat pump and hot water system according to claim 6 wherein said zero-load temperature difference Δ

T_Z is on the order of -13 degrees F. (7.2°

C.).

8. Method of operating a heat pump and hot water system according to claim 5 wherein said operating speed S_P is obtained at the time during said operating cycle when said outdoor temperature equals a predetermined temperature.

9. Method of operating a heat pump and hot water system according to claim 5 wherein said operating speed S_P is obtained at the time during said operating cycle when the difference between said outdoor temperature and said indoor temperature equals said reference temperature difference Δ

T_R.

10. Method of operating a heat pump system that is capable of providing heating or cooling to an environmental comfort zone wherein said heat pump system includes a variable speed compressor whose operating speed is controlled to vary with an imposed heat transfer load on the system;

controller means providing a speed control signal to the compressor to control its speed, the speed control signal being supplied under normal conditions at a normal speed value to operate the compressor at a normal condition speed; and

demand limit signal receiver means coupled to the controller means to receive a demand limit signal to initiate power limiting the method comprising supplying said speed control signal at said normal speed value when said demand limit signal is not being received by said receiver means; and

supplying said speed control signal at a reduced value below said normal speed value when said demand limit signal is being received.

11. The method of claim 10 wherein said reduced value is a predetermined fraction times the normal speed value.

12. The method of claim 10 wherein said compressor is operated at a speed that is substantially proportional to said heat transfer load.