Looking for some ideas on what to use to create a pressure sensor to better control the defrost cycle on a heat pump. Most heat pumps, including mine are dumb when it comes to defrost cycles. They have a temperature sensor that that sits in contact with one of the coolant lines. The sensor is connected to the board on the heat pump. When the sensor gets to 32F or lower the board starts a timer, adjustable from 30 min to 90 min. At the end of that timer if the temp is still 32F or lower it goes into defrost mode for a few minutes. To me that is a waste if the unit doesn't have frost on it.
What I want to do is put some kind of pressure sensor inside the heat pump that detects a pressure difference indicating the fins of the heat pump are actually freezing up thus letting less air through. A CFM sensor might work as well.
The arduino would monitor the sensor and turn a relay on if needed and then and only then would the heat pump go into defrost. So basically I want an added sensor to control the defrost cycle. I have seen other methods on the internet but none that are DIY. Most people want to make money off of this stuff and Ii don't see why if it's something I can do myself.
Once I find out which sensor will work I can do the rest. If no one has any ideas I may just order a few different sensors and play with them to see what I can come up with. If someone has already done this with an arduino can you point me in the right direction?
When the sensor gets to 32F or lower the board starts a timer, adjustable from 30 min to 90 min. At the end of that timer if the temp is still 32F or lower it goes into defrost mode for a few minutes. To me that is a waste if the unit doesn't have frost on it.
So you want to detect frost?
How does this detect frost?
What I want to do is put some kind of pressure sensor inside the heat pump that detects a pressure difference indicating the fins of the heat pump are actually freezing up thus letting less air through. A CFM sensor might work as well.
A pressure difference between what and what?
How will that detect frost?
OK, so picture an outside heat pump unit. they are mostly made up of a radiator that wraps around the whole unit with a big fan in the top of the unit. When it is in heat mode the fan kicks on and blows air up which pulls air through the radiator. If the radiator is clean and clear there should be little pressure difference inside the unit. If the radiator is blocked partially or fully there should be a notable pressure difference. I am thinking I could measure that difference to see if the heat pump actually needs to defrost.
I was thinking of using a differential pressure sensor like the MPX5500DP or MPX5100DP but not sure which to get. I am at around 3000 feet about sea level which is normally around 113 kPA. I am leaning towards the MPX5500DP to test with. If I use this sensor I could run one port outside the pump and one port inside the pump.
So I settled on the MPXV5004DP to test with. I dont think the pressure difference will be that great but will be a little different so I needed something a little more sensitive. Check out this page: http://www.energyvanguard.com/blog/74297/Why-Are-Heat-Pumps-So-Dumb-About-Frost and notice he says a pressure difference of .35 inches of water which is only .087kPA which isn't much. The pressure sensor he is using is on the same principle but higher priced. We will see.
Hi,
Okay, INSIDE the radiator housing, pressure difference between inlet and outlet.
Yes the DP looks good with two inlets to give pressure diff.
You could set the controller up to display a count of some sort to let you know how often it has defrosted, for diagnostic purposes.
You can also set it up so that a high pressure diff without the freezing temp, or prolonged high press diff means a possible obstruction in the airflow.
