ASHP: DHW and heating power consumption?

[HHboxmoor]

Hello.

Complete beginner question here.

 

I've had a Vaillant AroTherm 5kw plus installed recently on a 3 bedroom end-of-terrace house with a conservatory. Heat loss calculated around 4.4 kW.

Hot water tank is a unistor 180L.

 

Question is:

My system is saying the power consumption for DHW is almost 5x larger than my power consumption for heating.

 

Does this make any sense?

 

What would be the expected ratio between consumption for DHW and  heating?

[SteamyTea]

Water takes 4.2 times as much energy, per kilogram, to heat up than air.  Air density is 1.25 kg/m³, water 1000 kg/m³.  The Specific Heat Capacity of air is 1 kJ/kg.K, water is 4.2 kJ/kg.K.

It is also heated to a higher temperature i.e. 50°C rather than 20°C, then there is the associated temperature differences.

Mains water will enter the house at around 8°C this time of year, air around 5°C, though that can go lower i.e. -10°C.  So the DHW will have a deltaT of 48K, the air in the house between 15K and 30K.

If it is a sunny day, then there is some solar gain in the house, that contributes nothing to the domestic hot water.

There is also the question of how much DHW you use, it is easy to use more than you think.

The legionella cycle may also be permanently on, which makes the CoP of the heat pump effectively 1, rather than 3.5 or better.

And then there is the time period.  I would think it was a bit high over the last week or so, but over the year probably about right.

 

Do you have a breakdown of the actual numbers?

[Conor]

^tl;Dr

 

What temp have you the hot water set to and is there a immersion heater involved?

[ReedRichards]

17 hours ago, HHboxmoor said:

 

What would be the expected ratio between consumption for DHW and  heating?

 

If you have an Energy Performance Certificate that should estimate the heating and DHW power requirements.  In my case, the estimated DHW requirement was 22% of the space heating requirement but the SCOP for DHW was a bit worse.   So very roughly 20% of power used for DHW, 80% for heating.