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ferox 10-21-20 01:51 PM

Inverter Ac converting into air-water heat pump
My current setup is an 24000btu R22 external unit.
This is heating my 1000L plastic tank once a day, which is insulated with 10cm of extruded polystyrene. Inside the tank I have 10mm copper tube/ 20m for heat transfer.
To have the best efficiency I programmed to start the pump once at 2PM when the outside temperature is the highest.

In the summer 20min of running heating the tank for 24 hours need.
In the winter if the temperature is dropping to 5degC it runing 1, 5 to 2 hours. Under 5 C I need to heat with an electric heater.

Now I want to improve something and extend it to house heating too, not just hot water.

I want to change the external unit with an inverter one.
The idea is simple, not so simple to do it.

I have 2 options:
1. Buy a new heat pump - no fun, spending lot of money
2. Converting an inverter AC unit - lot of chalanges, price is almost 10th of the new one + time spent for fine tuning. I have this idea from long time ago.

I have some knolege about automations, so I can jump in.
My passive house need is 5kW thermal heat, I guess one 18k unit will be fine. This thread can be used for bigger needs.

The chalange:
1. Install the external unit- easy
2. Connect the coil or one heat exchanger to the unit - easy. I prefer heat exchanger.
3. Controller setup
A. Use the indoor PCB and find a way how to cheat to have the needed control of the outside unit
B. Learn how to send specific command to the outdoor unit and build a simple arm based controller
C. Maybe sombody did it an I don't know
D. Buy a ready-made controller with 0-10V input - tried to search but hard to choose

Now I'm writing from the phone, I will put pictures of actual setup later. I will have more updates.

Have a nice day

Sadashi 10-25-20 04:51 AM

2 Attachment(s)
What do you want to achieve when you said that you want to control the outside unit of the inverter ac ? Do you want to control the indoor temperature , keep a fixed flow temperature , or what ? As you see from the pictures , I'm using a 24k btu inverter unit to heat my house of 126 sqm , located in Buzau , Romania . Is your house located in Oradea ? Good luck with your project !

Ps : on my computer the pictures look fine , they don't need to be rotated . I don't know why they've been attached this way and I don't see the option on ecorenovator to rotate them so they look normal .

ferox 10-25-20 10:24 AM

Hi Sadashi!
Yo have a nice setup, you did it! Exactly as I want to do it.
My goal is to control the power of the outside unit, than I can keep a fixed flow temperature.
Can you share with us how you control the water temperature? In that case I don't need to reinvent the wheel. I have some ideas but always it is a risk that is not working as intended.
My 140sqm house is located in Oradea, where the weather is not so extreme as in the rest of the country.

Best Regards,

ferox 10-25-20 10:42 AM

6 Attachment(s)
Some pictures from the old inefficient setup.
External unit was modified to be able to have cooling for defrost proposes connected directly to the coil which is in the bottom of the tank. Was installed 7 years ago, working good, controlled with Arduino and Blynk app for remote control and visualizing the temperatures with the nice charts.
The plan is to upgrade with the latest inverter technology for heating the house.

Sadashi 10-25-20 01:03 PM

Inverter control
I'm afraid that I will disapoint you with regards to controlling the inverter unit to be able to keep a certain flow temperature . I'm not saying that it's not possible , but for me it wasn't a must , as my system the way it's been setup ( with radiators ) doesn't required a certain temperature , it varies depending on the indoor temperature . The inverter unit modulates the power output to meet the set temperature that I'm asking from it , so the flow temperature varies .

ferox 10-25-20 01:51 PM

I understand. You are using the original controller.
Is the easiest way of doing, just instead of internal air heat exchanger is an water HX.
In the same way I can put the temperature sensor of the air to the floor heating, in that case I can go just with temperature lower than 30degC.
Maybe I can find a way to cheat the room thermistor input.
How many sensors has your internal board, did you connected to HX?

Sadashi 10-25-20 02:23 PM

Indoor sensor .
If you have underfloor heating , then you can put the indoor air sensor on the return flow pipe and set your indoor temperature to 30C from the remote control , this way if delta T is 5C between supply and return , then you should have 35C on the flow pipe . I have only one thermistor on the brazzed plate heat exchanger .

ChetT 10-26-20 09:40 PM

Water temp
I've been thinking of using a similar system for my underfloor heating. Can either of you tell me how high a temperature can you heat the water? I need to add 15K BTU and I need to heat water to 125F. Is that possible?

BTW nice job on that coil.

Sadashi 10-27-20 12:47 AM

It is possible
I have a dhw tank of 300 litres , and the water temperature can reach at the top of the water tank 140F ( 60C ) , so it is possible to obtain that temperature , but it is limited on the volume of water that you have in your underfloor heating . It depends where is your house located , if the winters are not that harsh and there isn't a high humidity area when the outdoor temperatures varies between 40F and 25F ( it defrosts more often ) , then you should be ok .

ferox 10-30-20 08:07 AM

Based on options that I have, I choose option 1 is more likely for me
Option 1 : buy new heat pump Mitsubishi 7,5kw, 5kW not available.
- eazy installation
- if I want to sell the house is better
- service friendly, not need my assistance

Option 2:
- finding the right unit is not easy
- hi COP unit rented to 5 is expensive
- lot of chalanges
- warranty lost

Option 3:
- gas boiler is half price of heat pump
- gas price is more volatile than electric
- cannot be used with PV panels
- yearly authorized person verification needed

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