How do users know what kind heat pump should buy? Such as air source heat pump, geothermal source heat pump, water source heat pump and swimming pool heat pump. 
      Air source heat pump working condition is from -25C to +40C. And the efficiency is affected by air temperature greatly. Colder weather, lower efficiency. So air source heat pump is suitable for the place where air temperature is above -25C.. 
  Geothermal source heat pump is: bury pipe in the garden ground, and water in the buried pipe deliver heat from soil to heat pump, heat pump transfer heat to house or hot water. Because soil temperature changes little and about 10C all the year, so that geothermal source heat pump gives constant and high efficiency all the time. If there is enough place to bury pipe, geothermal source heat pump is the best choice. But to install geothermal source heat pump cost higher than air source heat pump. 
  If there is lake or river beside, water source heat pump can be a good choice. But the water can’t be ice up in winter, otherwise water will can't cycle. 
  How to select heat pump for house? If cool house, you can calculate the total cooling load like this: average cooling load is about 220w/m2, so the heat pump total cooling capacity should be larger than your house cooling load. 
  If you heat house, the average heating load is about 100w/m2, so the heat pump heating capacity should be larger than your house total heating capacity. 
  If you use heat pump supply hot water for shower, 3.5kw to 7kw heating capacity heat pump should be ok for a common family. If a large family, you can consider a larger model. 
  If you need both heating house and hot water, the heat pump heating capacity should be above two heating load add together.