Evaporator Design-Air Source Heat Pump for water heating

[anup]

Dear Technocrats,
I am designing air source heat pump for water heating for Indian conditions
As a first step, the evaporator is designed. While designing, I have considered two ambient conditions, delta T across evaporator is 46.4 deg. F (8 deg.C.) and R.H. 25%
The inputs and output calculations are attached.
Kindly guide me to design it perfectly.
How much delta T should be designed for getting optimum COP?
If you face any problem whie reading below calculations, I have attached the same as an attachment.

Evaporator Design

Sr. No. Parameters Units Case 1 Case 2
a Input
1 Inlet Air Temp deg. F 89.6 68
2 Outlet Air temp deg. F 75.2 53.6
3 R.H. at inlet air temp considered 25% 25%
4 R.H. g/m3 33.83 17.3
kg/m3 0.03383 0.0173
5 Refrigerant type R 22 R22
6 Heat Load Kw 20.15 20.15
7 Air Flow CFM 3431 3711
m3/hr 5830 6305
8 LMTD deg. F 68.97 46.67
9 Tube Material Cu Cu
b Output
1 No. of tubes nos 120 180
2 Tube length mtr 1.2 1.2
3 Tube OD mm 12.7 12.7
4 Tube ID nos 8.5 8.5
5 No.of Fins/inch nos 13 13
6 No. of rows nos 3 3
7 No. of passes nos 14 14

[Lc_shi]

Hi Anup,
It's very good to share your design with us. I want to ask something first and then maybe I can say something.
What's your design standard? refrigerant side and air side. I mean ,what about te tc,superheat and subcool,these one decide the COP.
is there any standard for air source hp in your country?
I'll make some calculation later

good luck

rgds
LC

[anup]

Dear LC,
Thanks for your reply.
I suppose te is evaporating temp and tc condensing temp. If so, then
Te - 44.96 F
Tc - 129.2 F
We are not going for superheating as well as subcooling temp
Regards
Anup

[NoNickName]

Te - 44.96 F
Tc - 129.2 F

You lucky guy. Still, somebody wants air to water heat pump in europe.... asking for high COP....

[anup]

In India, there is no standard for air source heat pump. Infact I would appreciate, if our friends mail me the standards for air source heat pump, which I can lobby with the government. As on today, there is no player in India in air source heat pump

[Lc_shi]

Air source heat pump design condition is : te=2C and tc=50C in our place. Maybe India's ambient temp is different. How about the summer weather in india? Per Q=KF(LMTD），what's your K and F? If possible,pls lower the condenser temp,which help to increase COP.
BTW,your terminal is by air or water?

regards
LC

[Lc_shi]

You design the heat pump only for water heating? I refer to your title again.

We are not going for superheating as well as subcooling temp

Why ? pls explain

regards
LC

[NoNickName]

If Europe, air source heat pumps are installed in countries where the ambient can be as cold as -5°C (or colder, but it won't work). In that case evaporating temperature can be -12°C.
In a heat pump, Te is uncontrolled, and is slave of warm water thermoregulation probe, until either it doesn't produce any more warmth than it absorbs for defrosting or it stops by low pressure cut out.
But India is a whole different story.