Electric Spa Heater Recommendations and piping arrangements

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Kram21

Member
Feb 14, 2021
12
Perth
Hi

I have decided to go down the owner builder pool route. Ive produced a design (below) which has now been approved by council. The design consists of 20'x13' and 4' to 6" deep (9,000gal) below ground gunite pool an attached above ground spa approx 7'x6' (550gal) with a live edge to 3 sides spilling into the pool.

However I have got into a cycle of analysis paralysis with regard to the spa heating system and general system piping arrangement and was hoping to get some closure on here!!

I was proposing to heat pool using a 17kw Pentair VX heat pump on a dedicated circuit with a vsd pump, sand (glass) filter, chlorinator. The pump would use a number of actuated valves to return water back to the pool, 4 laminars (on demand) and spa overflow (on demand).

For the Spa I was looking at natural gas Pentair MasterTemp 125, in a dedicated circuit with small fixed speed pump, cart filter, chlorinator. A high volume fixed speed pump and blower for the spa bubbles.

However after reading through the Mastertemp125 installation manual I will need to run 1.5 to 2" copper pipe from the gas meter to the pool equipment area approx 120' away. My plumber has said material and labour costs will be $$ and the cost to operate such a heater will also be $$. He has instead suggested using the funds to purchase either a second heat pump or a direct element electric heater particularly as I have such a large PV system.

As I mention Id be really appreciative of any suggestions for equipment and piping arrangements as well as successful heating options.

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I have just received approval to install 20kw of photovoltaic panels which should generate an average of 90kw per day. There it also probab;ly makes sense to maximise electric heating.
 
Have you looked at the specifications for the electrical resistive heaters you are considering? Amperage input and BTU output? Tell us what specs you are considering.

How many gallons of water in your spa?
 
What is the largest heater you think your PV system can run?

You only plan on heating your spa during daylight hours when your PV is generating or do you have battery storage?

What spa temperature rise do you expect in what time?

Will you cover the spa and keep it heated or need the heater to raise the water temperature from ambient to spa temperature in a reasonable time?
 
Ive just found this calculator for heating water which is pretty handy.

Water Heating Calculator for Time, Energy, and Power

The calculators on this page compute how long it takes to heat water, how much energy is consumed, and how much heating power is required.
bloglocation.com bloglocation.com

Anyhow would appear a 18kw/h (61416btu/h) electric heater would take 67 minutes to heat the spa 10degC to 38degC which isnt too bad if I remembered to switch it on an hour before I need. This heater is approx 25% cheaper ($1000) in price than a 125 model gas spa heater. However the 125 gas heater at twice the btu/h (125000) would heat the same volume of water in just 33minutes.

I have checked my gas bill and my all in cost of gas supply per unit (m3) is $0.13, therefore the 125 gas heater would use 3.5units/h =45c/h running cost but this seems too low surely?
 
So your PV system can provide 415 volts, 3 phase, 25 amps power?

Natural gas is usually reasonably priced. The NG heater will be a $1,000 additional one time cost. What is the cost for all the PV to feed an electrical heater?
 
What is the largest heater you think your PV system can run?
Ill be installing 2x SMA 10kw 3 ph inverters
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You only plan on heating your spa during daylight hours when your PV is generating or do you have battery storage?
No battery storage initially as government arent rebating but expect in next 12-18ths. Would be looking at 2 x14kw batts

What spa temperature rise do you expect in what time? If I had a constant return into spa from heat pump during day and maintained 28degC it would only require 10degC increase. However unsure if this is realistically possible.

Will you cover the spa and keep it heated or need the heater to raise the water temperature from ambient to spa temperature in a reasonable time? The intent would be to get a custom spa bubble type cover and supply spa with constant supply from the heat pump during the day. Looking at the table below for the Pentair HP table below it may only draw 2.5-3kw/h (8500-1000btu/h) to heat a 2 degC over night heat loss.

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ajw22 said:
So your PV system can provide 415 volts, 3 phase, 25 amps power?

Natural gas is usually reasonably priced. The NG heater will be a $1,000 additional one time cost. What is the cost for all the PV to feed an electrical heater?
Click to expand...
20kw PV system will $6k out of pocket as I have friends in the industry, but then intent was not use it all on the pool /spa!

Out of interest what is the all in cost ie supply and usage of natural gas in the US and how much do you estimate is spent heating your pool? If my calculation is correct on the earlier post ie 3.5m3/h of NG for 125 heater it appears its not as bad I initially thought.
 
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