A unitary heat pump air conditioner (unitary hpac), comprising: - a plate-type hpac heat exchanger having a plurality of plates stacked and hermetically sealed between an upstream end plate and a downstream end plate, defining: - a first heat exchanger portion for a refrigerant flow and a hot side coolant flow having a lower temperature than the refrigerant flow, wherein said refrigerant flow is in non-contact thermal communication with the hot side coolant flow, whereby heat energy is transferred from the refrigerant flow to the hot side coolant flow; - a second heat exchanger portion for a refrigerant flow exiting from said first heat exchanger portion and a cold side coolant flow having a higher temperature than the refrigerant flow exiting from said first heat exchanger portion, wherein the cold side coolant flow is in non-contact thermal communication with the refrigerant flow, whereby heat energy is transferred from the cold side coolant flow to the refrigerant flow; - an internal heat exchanger portion for the refrigerant flow exiting from said first heat exchanger portion before being received by said second heat exchanger portion and a refrigerant flow from said second heat exchanger portion before exiting said second heat exchanger portion, - wherein the temperature of the refrigerant flow exiting said first heat exchanger portion is higher than temperature of the refrigerant flow from said second heat exchanger portion, - wherein the refrigerant flow from said first heat exchanger portion is in non-contact thermal communication with the refrigerant flow from the second heat exchanger portion, whereby heat energy is transferred from the refrigerant flow exiting from said first heat exchanger portion to the lower temperature refrigerant flow from said second heat exchanger portion; characterized in that said internal heat exchanger portion is sandwiched between said first heat exchanger portion and said second heat exchanger portion, thereby forming a single unit integral plate-type hpac heat exchanger. - a plate-type hpac heat exchanger having a plurality of plates stacked and hermetically sealed between an upstream end plate and a downstream end plate, defining: - a first heat exchanger portion for a refrigerant flow and a hot side coolant flow having a lower temperature than the refrigerant flow, wherein said refrigerant flow is in non-contact thermal communication with the hot side coolant flow, whereby heat energy is transferred from the refrigerant flow to the hot side coolant flow; - a second heat exchanger portion for a refrigerant flow exiting from said first heat exchanger portion and a cold side coolant flow having a higher temperature than the refrigerant flow exiting from said first heat exchanger portion, wherein the cold side coolant flow is in non-contact thermal communication with the refrigerant flow, whereby heat energy is transferred from the cold side coolant flow to the refrigerant flow; - an internal heat exchanger portion for the refrigerant flow exiting from said first heat exchanger portion before being received by said second heat exchanger portion and a refrigerant flow from said second heat exchanger portion before exiting said second heat exchanger portion, - wherein the temperature of the refrigerant flow exiting said first heat exchanger portion is higher than temperature of the refrigerant flow from said second heat exchanger portion, - wherein the refrigerant flow from said first heat exchanger portion is in non-contact thermal communication with the refrigerant flow from the second heat exchanger portion, whereby heat energy is transferred from the refrigerant flow exiting from said first heat exchanger portion to the lower temperature refrigerant flow from said second heat exchanger portion; - a first heat exchanger portion for a refrigerant flow and a hot side coolant flow having a lower temperature than the refrigerant flow, wherein said refrigerant flow is in non-contact thermal communication with the hot side coolant flow, whereby heat energy is transferred from the refrigerant flow to the hot side coolant flow; - a second heat exchanger portion for a refrigerant flow exiting from said first heat exchanger portion and a cold side coolant flow having a higher temperature than the refrigerant flow exiting from said first heat exchanger portion, wherein the cold side coolant flow is in non-contact thermal communication with the refrigerant flow, whereby heat energy is transferred from the cold side coolant flow to the refrigerant flow; - an internal heat exchanger portion for the refrigerant flow exiting from said first heat exchanger portion before being received by said second heat exchanger portion and a refrigerant flow from said second heat exchanger portion before exiting said second heat exchanger portion, - wherein the temperature of the refrigerant flow exiting said first heat exchanger portion is higher than temperature of the refrigerant flow from said second heat exchanger portion, - wherein the refrigerant flow from said first heat exchanger portion is in non-contact thermal communication with the refrigerant flow from the second heat exchanger portion, whereby heat energy is transferred from the refrigerant flow exiting from said first heat exchanger portion to the lower temperature refrigerant flow from said second heat exchanger portion;