I was wondering if people could give me a little advice before I take the plunge and install a heatpump.

My chief reason is to cut down on the consumption on my off-grid PV system and hopefully increase the capacity of the hot water system.

Noise: Looking at heat-pump datasheets, they list things like 52dB. Looking at what 52dB means, you get: "normal level of speech, rainfall, refrigerator, light traffic and a residential street.", which is about as descriptive as softer than a hairdryer but louder than rustling leaves. Since the unit has to be installed outside, the most ideal place to mount it would be under the eaves of the upstairs bathroom close to the geyser: a spot that is unfortunately pointing directly at neighbours and right next to the bedroom and lounge windows which will end up with a particularly low "Wife Approval Factor" and high "Neighbour annoyance factor". Currently I am considering either mounting it in the utility room and then building a massive amount of ducting to try and vent it to the outside, or mounting it on the wall and putting some sort of fibre-cement board and insertion rubber sound shroud around it. Anyone have any advice or other suggestions?

Size: The current geyser is around 3kw, so I have room for around a 11kw heatpump (looking at the power consumption numbers from datasheets). Should I install one 11kw unit, or 2x 5.4kw units? I am aware that there is a price difference, but it will allow me to run a single unit in the event that my PV panels are experiencing low production. If i install 2 units, do i run them in series or parallel?

 

 

 

5 minutes ago, NotDave said:

I was wondering if people could give me a little advice before I take the plunge and install a heatpump.

My chief reason is to cut down on the consumption on my off-grid PV system and hopefully increase the capacity of the hot water system.

Noise: Looking at heat-pump datasheets, they list things like 52dB. Looking at what 52dB means, you get: "normal level of speech, rainfall, refrigerator, light traffic and a residential street.", which is about as descriptive as softer than a hairdryer but louder than rustling leaves. Since the unit has to be installed outside, the most ideal place to mount it would be under the eaves of the upstairs bathroom close to the geyser: a spot that is unfortunately pointing directly at neighbours and right next to the bedroom and lounge windows which will end up with a particularly low "Wife Approval Factor" and high "Neighbour annoyance factor". Currently I am considering either mounting it in the utility room and then building a massive amount of ducting to try and vent it to the outside, or mounting it on the wall and putting some sort of fibre-cement board and insertion rubber sound shroud around it. Anyone have any advice or other suggestions?

Size: The current geyser is around 3kw, so I have room for around a 11kw heatpump (looking at the power consumption numbers from datasheets). Should I install one 11kw unit, or 2x 5.4kw units? I am aware that there is a price difference, but it will allow me to run a single unit in the event that my PV panels are experiencing low production. If i install 2 units, do i run them in series or parallel?

 

 

 

Just my input. Ensure the heat pump used some kind of loading valve to prevent or reduce the mixing of cold and hot water. Secondly bear in mind you want your HP within 5m of the geyser. I would use 1 x 5kw unit. In summer it heats as fast as a element at less than 50% the power which will be good for your PV system. In winter it might be a strain if switched on during the night. Having a 11kw unit to me is wasting power in order to achieve very fast heating. If capacity(storage) is needed then rather increase the geyser size or put 2 next to each other to the 5kw unit.

Lastly we will not not install an aircon due to noise but why would a HP not be installed as the noise is the same. Yes you can hear it but it is not load that it presents a problem.

Ensure about 250mm free space behind the unit against a wall.

After 9 years using mine I will do the same if I had to choose.

11KW is surely the pool heat pump, it does not reach 55degrees nor is it suitable for heating your geyser. 

Get one heatpump and put your geysers in series and heat both of them at the same time. A single heatpump can easily heat 400 litres of water

I have a 150 litre geyser.

My heatpump(4.7KW drawing about 1.3KW) uses about 1.7 - 2KWh to heat the water from about 25 degrees to 55 degrees (in 1h 40min) in the middle of winter running at 11 when my solar is producing nicely. If you run it from 4am when it is cold outside it still heats the water, it just uses about 2.0 - 2.4KWh and takes an extra 30 minutes. Granted in pretoria the night time temps sit around 2 degrees and up. In summer it only uses about 1KWh in 45 minutes.

Asked the technical department at ITS some questions and they simply ignore my emails so not very happy with their customer service at this moment.

 

10 minutes ago, iiznh said:

11KW is surely the pool heat pump, it does not reach 55degrees nor is it suitable for heating your geyser. 

There are some 11kw commercial units out there. They are not common in residential installations, but I get your point, there not that many situations where you need to boil a 150L geyser in the middle of winter in 45min or less.

During the winter I run my 150L geyser in cycles from 10h00 to 15h30 to avoid drawing on the batteries and it consumes about 5kw per day. If a heatpump uses half the draw, it should extend the usage window from 09h00 to 16h30. From my current usage patterns, I have about 10kwh of unused solar potential after the batteries are full and the geyser is boiled, which would probably increase to 12kw or 13kw with a heatpump. With napkin math, its close to an additional 800L in hot water that can be used to take the edge off in heating the house in the winter, though that's probably a whole different can of worms.

 

35 minutes ago, NotDave said:

close to an additional 800L in hot water that can be used to take the edge off in heating the house in the winter

Ah, I understand.

Why not look into a air-to-air heatpump (some aircons can run reverse cycle to generate heat). That way you can have cool air in summer and nice warm air in winter. Then again you might want to store the heat for later use and in that case a hot water battery makes perfect sense.

The heatpumps are not very loud. I guess if it is right next the the neighbours window they might complain. I have to walk outside to be able to hear it

Edited July 6, 20223 yr by iiznh

This puzzle has been boggling my mind since yesterday.

More Napkin Math (probably very wrong, so feel free to point it out)
The specific heat (the amount of energy stored per unit) of water is about 4.18 Joule per gram per degree Celsius.

Working backwards, if the temperature difference in the water is 33 degrees (22 minimum temperature in the house, 55 max water temperature in the storage tank) with an 800L water tank, the system will store roughly

= (specific heat in joule) x (temperature difference in Celsius) x (weight of water per litre in grams) x (storage capacity in litre)

= 4.18 * 33 * 1000 * 800

=  110 million joules.

1Kwh of energy = 1 joule * 60 seconds * 60 minutes * 1000 (kilo) = 3,6 million joule. Thus, a 2.8Kwh lipo is going to be around 10 million joules (2.8 as opposed to 3.5 as there is a 80% depth of discharge limit).

Even if the lipo battery -> inverter -> air-air heatpump / aircon is 100% efficient, and the heatpump / aircon has a coefficient of performance of 1:4 (generoud in cold climates), its only going to deliver about 40 million joules of heat, which is only about 36%, which works out to almost exactly 3 pylontech US3000s (R54k) or 4x 200L geysers from chamberlains (R26k). Granted, I have not taken into account the loss of heat due to insufficient system insulation, but at the same time I didn't take into account the loss of energy as part of the charge-discharge cycle in batteries.

TL;DR: it seems like storing heat in a 'hot water battery" is roughly half the cost compared to storing it in Lipo Batteries, at the expense of not being able to use said energy for anything other than heating purposes.

 

 

Ya it could be a matter of finding some work for the PV and storting 800L of hot water when you actually need only 300L per day 🤔🤔

What worked for me years ago to get details from ITS was to phone the head office in CoCT. Very helpful engineers assisted me to decide on buying their heat pump. 😀😀😀😀