Eco Self Build - System Design

[deancatherine09]

Hi all,

We are looking for opinions and advice on the systems we have currently specified for our build.

 

It’s a near-passivhaus build, with MBC timber frame on an insulated raft foundation.  Our predicted SAP rating is 102.

The Primary fuel will be electric, there is no gas in the village, and we don’t intend to install LPG or Oil.

 

We plan on having a large solar array (just waiting to DNO approval at the moment) and Tesla Powerwall – using the Octopus Tesla Electricity tariff, so power diverters and smart energy management are off the cards.

 

We are looking at having a Sunamp Heat battery, in place of a hot water cylinder, and heating the house will be Ground floor UFH, and potentially using the MVHR air.

 

We would like to run the ASHP in reverse in summer to cool the ground floor slab and the MVHR – but would still need to run it forwards to charge the heat battery.

 

The Sunamp would be the HP version, which has primary input of (High Temperature) ASHP, and a backup option of mains electricity.

This suggests 2 possibly options for Hot water in summer:

1)      Run the ASHP in Heating mode when necessary to charge the Sunamp – and disconnect the UFH and MVHR art this point

2)     Always run the ASHP in cooling mode when actively cooling, and charge the Sunamp from electricity (surplus from the solar in summer).

Sunamp specify ASHPs to work with the heat battery, one being the Valiant aroTherm which is reversible.

 

We wonder if anyone has done this sort of configuration and can offer advice on how they achieved it / information on how it has performed.

Is there a valve / manifold product available that could handle isolating the output of the ASHP from the Sunamp or the Heating elements depending on which mode is being used on each?

 

Our main concern at the moment is that we like a cool bedroom (17 – 18 degrees) and want to make sure we can achieve this year round with the systems we install.

 

Here is a simple diagram of the system we are trying to describe with this post.

[Nickfromwales]

Whether SA or UVC, you defo do NOT want to be taking space heating from the point you show it entering "valve". Who's specified this?

Also, having a SA means running at very high temps to get a speedy reheat of the DHW.......which PCM is the current flavour? 58?

[JohnMo]

You are making life complicated for yourself.  Keep it simple.

 

Not sure I would do a SA with a heat pump, just use an UVC. 

 

Take heating and cooling flow from heat pump via a buffer cylinder.  Feed to mixer valve /pump at manifold (low temp).  Run downstairs as a single zone.

 

Run DHW cylinder at 46-48 degC

UFH flow should be circa 26-30.

 

Don't limit yourself to one pump manufacturers heat pump. Valiant heat pumps use propane, so limits your placement of the outdoor unit.  Also I believe Vaillant unit is only reversible with a £300 (should be £1) resister in a plug.

[Dan F]

40 minutes ago, JohnMo said:

Not sure I would do a SA with a heat pump, just use an UVC. 

Agree. We came to same decision.  Big avantage of SA is the minimal space it takes up, but it has other issues and if you want 300L+ equivalent capacity you need 2 of them which works out a lot more money than a 300L UVC.  Issue I saw were:

- Hard to tell state of charge.

- Requires higher ASHP flow rate than you'd typically use with UVC

- Unless you use 70C flow (i think) to charge you don't get the full quoted capacity.

- When i looked a couple of years ago they were using ASHP manufuatuer specific controlers!

(they do make more sense, IMO, if you plan to charge with electicity rather than ASHP and are short on space)

 

40 minutes ago, JohnMo said:

Don't limit yourself to one pump manufacturers heat pump. Valiant heat pumps use propane, so limits your placement of the outdoor unit.  Also I believe Vaillant unit is only reversible with a £300 (should be £1) resister in a plug.

There are some placement limitation, but they aren't very significant and have been relaxed since the original version of their manual. @m0dellergot resistor for £5 from link I shared.

[Dan F]

2 hours ago, deancatherine09 said:

 We plan on having a large solar array (just waiting to DNO approval at the moment) and Tesla Powerwall – using the Octopus Tesla Electricity tariff, so power diverters and smart energy management are off the cards.

If you want a powerwall you need to reserve one now, they are in very short supply with most installers now having waiting lists and quoting very long lead times.  We've given up and will likely go down the Victron route instead.  Likely to be bit more expensive, but more flexible/programmable.

 

2 hours ago, deancatherine09 said:

 We are looking at having a Sunamp Heat battery, in place of a hot water cylinder, and heating the house will be Ground floor UFH, and potentially using the MVHR air.

Heating/cooling via MVHR is not required on GF if you have UFH in slab.  On the first floor Comfopost can add some heat, but you are looking at a couple of kW max (assuming less efficient 55C ASHP flow)

 

2 hours ago, deancatherine09 said:

 We would like to run the ASHP in reverse in summer to cool the ground floor slab and the MVHR – but would still need to run it forwards to charge the heat battery.

That works fine, as long as your ASHP supports cooling.

 

2 hours ago, deancatherine09 said:

 The Sunamp would be the HP version, which has primary input of (High Temperature) ASHP, and a backup option of mains electricity.

This suggests 2 possibly options for Hot water in summer:

1)      Run the ASHP in Heating mode when necessary to charge the Sunamp – and disconnect the UFH and MVHR art this point

2)     Always run the ASHP in cooling mode when actively cooling, and charge the Sunamp from electricity (surplus from the solar in summer).

Sunamp specify ASHPs to work with the heat battery, one being the Valiant aroTherm which is reversible.

This logic would all be managed by the ASHP controller.   Surely, allowing the ASHP contoller to automatically switch to DHW and heat and UVC/SA and then return to cooling is simpler and more efficient that implementing a summer-only approach with your own controls.  You can still use a PV diverter if you want to, it's not either/or.  But, if you are on Octupus Tesla Plan you are not supposed to use a PV inverter, and there is nothing to gain from using one either.

 

2 hours ago, deancatherine09 said:

 We wonder if anyone has done this sort of configuration and can offer advice on how they achieved it / information on how it has performed.

Is there a valve / manifold product available that could handle isolating the output of the ASHP from the Sunamp or the Heating elements depending on which mode is being used on each?

I have everything you have decribed installed, aside from the SA.  Our build is also MBC with passive-slab.   The "valve / manifold product" is a 3-way diverter valve which is pretty standard and would be an assumed part of any ASHP install.  Where you go beyond a basic install is if you want/need different heating/cooling circuits running at different temperatures.

 

2 hours ago, deancatherine09 said:

 Our main concern at the moment is that we like a cool bedroom (17 – 18 degrees) and want to make sure we can achieve this year round with the systems we install.

If this is your goal, I would strongly recommend against MVHR for supplementaty cooling of bedrooms, it's just not suitable.  Even if you have overhangs and automated blinds, the cooling power from MVHR will only give you very minimal supplementay cooling and you definitely won't achieve these temperatures in the summer (unless you ground floor is cooled to 16C and you have blinds).  To achieve this you need fancoil units in the bedrooms. 

 

Edited August 15, 2022 by Dan F

[joth]

13 hours ago, Dan F said:

Our main concern at the moment is that we like a cool bedroom (17 – 18 degrees) and want to make sure we can achieve this year round with the systems we install

 

Have you considered building an upside down house? Assuming you like the living areas warmer than bedrooms, putting bedrooms on the ground floor and living areas above will give a major boost to the year round temperature balancing act.