ASHP Sizing - with data - and questions

[Tadpole]

Intro: We are (soon) building a Potton SIPS, 2 storey, pretty conventional house in north Wiltshire.  It will have ASHP, UFH downstairs mostly tile, upstairs carpet, MVHR, 3.6kW in roof PV facing SW, HW recirculating.
 
Data: 94 sq m ground floor @0.15, 210 sq m internal wall area @0.15, 90 sq m internal roof area @0.12, 16 sq m windows @0.94, 1.6 sq m Velux @1.00, 12 sq m bifolds facing SE @1.20, 4 sq m doors @1.00, 1.6 sq m Velux at 1.00

 

People: 2 active retirees, lots of guests that stay for a few days. We like to be able to hold 21-22deg in the winter, have plenty of hot water, enjoy the quiet when we sleep (ideally ASHP off between 2300-0700). Minimal, supportive automation is planned.

 

The above data plugged into Jeremy’s excellent spreadsheet reveals:

Monthly heat energy input (kWh) for minimum OAT between 1080 and 2049.
Total heat loss power (W) = 3311 for delta T = 25deg (-3 to 22)

 

Questions:
1.    How to convert all of the above into a suitably sized ASHP?
2.    How much to allow for DHW?
3.    What size HWC?
4.    Major brands seem to be favoured by those not confident with DIY – any brand / model suggestions?
5.    Is it really worth having wet UFH upstairs other than just the bathrooms?
6.    How best to inexpensively mitigate externally against overheating due to the bifolds?
7.    I am seriously considering a modest split AC unit in the master bedroom - any brand / model suggestions? 
8.    A more passive solution could be an electric Velux in the east-facing vaulted ceiling of the master bedroom – currently just 2 x electric Velux in the den/family room – to encourage purge – views?

 

If you have read this far – thank you. When we embarked on this (ad)venture I had no idea of the scope and variety of systems that are increasingly commonplace. With the help of this brilliant forum I think I now know most of the questions to ask and understand almost all of the responses.

 

As my requirements / ambitions are pretty conservative – almost mainstream – I hope these questions and the eagerly anticipated responses will be helpful for others.
 

[SteamyTea]

13 minutes ago, Tadpole said:

ideally ASHP off between 2300-0700

So in winter, with the windows closed, thick curtains drawn, and an ASHP drawing minimum loads on setback temperatures, do you really think that a properly sized, located and run, will be a real problem, or one you want to imagine may happen.

[JohnMo]

One thing to always bear in mind with heat loss calculations is the worst OAT is only for hours or maybe a day or two, maybe 5 to 7 days a year.  All the rest of the time the heat demand is lower.

 

Have attached MCS manual, that will start you in the correct direction on sizing ASHP and buffers etc.

 

1. Read manual attached

2. Two situations, you and wife, you wife and others.  Could you operate two cylinders, bring the second online when you have guests?  Save continuous heat loss etc.

3. 2 X 250 to 300l

4?

5 maybe not

6 internal or external blinds

7 LG or Mitsubishi seem quite good from what I heard

8 could work

 

You don't mention ventilation system?

Heat-Pump-Guide.pdf

[Tadpole]

@SteamyTea My only experience of heat pumps is one on a swimming pool in a Florida villa rental which burst into life loudly, early in the morning and was audible whenever it was running. Unfortunately, other considerations mean we will have the ASHP on the same side of the house as the "opened at night" windows of our bedroom. If you are inferring that a correctly designed solution will not have a noise impact then I'm ready for that.

 

@JohnMo thanks for the feedback and the document - very interesting

 

[ProDave]

Re the "off at night" thing.  that is down to careful system design and pipe routing.

 

I turn ours off at night for the same reason, BUT it is not the noise of the ASHP that bothers me, rather just the very gentle hum of the water circulating pump.  the circulating pump is in the plant room next to our bedroom and it's noise resonates through the pipes under our bedroom.  Had i anticipated this issue I could have avoided it by locating the pump  elsewhere and routing the pipes a different way.  The other bedrooms in the house do not suffer this issue.

[markocosic]

Appropriate shading first if possible / acceptable. That kills overheating due to sun but not overheating due to a sustained hot spell. Veluxes are fairly horrible from this point of view!

 

5 kW ASHP will heat the place with ease.

 

5kW (?) mini split AC to the upstairs landing (quieter than in bedroom and will pre-cool all upstairs rooms plus spill downstairs if allowed to do so; plus backs up the ASHP if it dies and can be run in parallel to reheat aggressively in a "just got home from hols" scenario) How bad will overheating be as is? Do you intend to cool it or just take the edge off hot spells in order to sleep? (with the window shut to keep the heat out)

 

Immersion can be used for faster reheat if guests rinse the hot water. On that odd occasion that you use loads. No need for dual cylinders.

 

To what degree is budget important? That probably dictates equipment choice as much as anything else. "Forever" house?