Air Handfling Unit with Integral DX Unit Problem.

[David OShea]

I have an Air Handfling Unit with Integral DX Unit that appears to have an issue on output. For some reason it seems to flatline at 50% of it's output duty. When calling for heating the DX Unit seems to ramp up and then quickly ramp down even though the heating demand has not been satisfied. If I'm calling for air to be pumped in at say 23oC it is only reaching about 19.5oC when the external temperature is at 4oC.

 

[willard3]

Hire an Engineer familiar with DX systems to troubleshoot this.

 

[GT-EGR]

Not sure your question is clear. Is this AHU a heat pump - is the heat provided utilizing the refrigeration cycle in reverse, or is it s DX cooling unit that maybe has electric heating?

First thing that comes to mind is that a heat pump does not heat very well when the outdoor temperatures get low - not due to capacity issues but due to the limitations of the refrigerant attempting to absorb heat in the condenser section from very cold outdoor conditions. So it's possible your unit is ramping up and attempting to start heating and then some refrigerant pressure/temperature safety is stopping it after a short period of time to protect the compressor. Check with the manufacturer and they usually post the heating capacity, but also include outdoor air limitations to get this capacity. Heat pumps installed in cold climates usually need a secondary source heat (gas, electric, separate baseboad) to handle the heating for the very cold months.

 

[Drazen]

why would you want 23 deg. air when outdoor temp is 40 deg.??!

As for quickly stopped heating, it's possible that unit enters defrosting cycle, which is particularly sensible at heating start-up. the older the technology, the longer defrosting cycle. many new units have bypass which makes defrosting cycle unnecessary or minimised.