Air source heat pump with MVHR?

[SteveB]

I have a bungalow which we renavated a few years ago including fitting a mechanical ventilation heat recovery system. I'm wondering if it is possible to incoperate an air source heat pump or replace the MVHR unit with an air source heat pump to heat the house.

Is this a stupid idea?

Does anyone make a combined unit?

Any advice welcome.

Cheers

Steve

[Gone West]

Hi, welcome to the forum. Yes I have a Genvex combined unit, but they only work in a very well insulated house. Why not leave your MVHR as it is and add an air to air heat pump to the house if that is the route you want to take. What is your existing heating?

[Dreadnaught]

Welcome to BuildHub!

 

Yes, they are available.Earth Save Products do one, for example. A BuildHub member who installed one had problems with noise a vibration as the combined unit was located in the attic near a bedroom.

 

As you may be aware, MVHR is generally not very well suited for heat delivery as the air speed is so very low. Ramping it up can easily cause noise in the ducting. Personally, because of this for space heating I am going for an ASHP heating under-floor heating (UFH) separately from my MVHR.

[SteveB]

We have a reasonably new combi boiler for heating and water. Its all raditors as we have concrete floors so underfloor heating was too much of a job. Insulation is about as good as we can get in a 1950s bungalow. All the doors and windows seal well.

[PeterW]

31 minutes ago, SteveB said:

We have a reasonably new combi boiler for heating and water. Its all raditors as we have concrete floors so underfloor heating was too much of a job. Insulation is about as good as we can get in a 1950s bungalow. All the doors and windows seal well.

So that isn’t a good candidate for a combined ASHP/heating as they can move about 2kW into the air flow and you will have a much larger heat loss I would expect. 

[Gone West]

43 minutes ago, SteveB said:

We have a reasonably new combi boiler for heating and water. Its all raditors as we have concrete floors so underfloor heating was too much of a job. Insulation is about as good as we can get in a 1950s bungalow. All the doors and windows seal well.

In that case I wouldn't change anything and if there are no problems leave well alone.

[SteamyTea]

There is nothing wrong in directly heating air, it is just the practicalities of it.

To heat a litre of air, by 1 °C, takes 1.2 J.

So if you have a total airflow of 10 litres/second, and you need to raise it by 10 °C, you need a power of 120 W.

Trouble is, you may need a lot more air and that gets noisy.

Edited September 3, 2020 by SteamyTea

[SteveB]

I wasn't thinking so much of using it to replace my convetional heating (which has got a smart control), more of maximising the heat recoved from the exiting air. If you take the warm air exiting and have an air to air heat pump surely that is more efficient than the MVHR heat exchanger.  And I guess it may be possible to use it for cooling in the summer.

 

[zoothorn]

On 03/09/2020 at 08:28, Dreadnaught said:

Welcome to BuildHub!

 

Yes, they are available.Earth Save Products do one, for example. A BuildHub member who installed one had problems with noise a vibration as the combined unit was located in the attic near a bedroom.

 

As you may be aware, MVHR is generally not very well suited for heat delivery as the air speed is so very low. Ramping it up can easily cause noise in the ducting. Personally, because of this for space heating I am going for an ASHP heating under-floor heating (UFH) separately from my MVHR.

I too have issues with boiler and system noise within the house, with my valiant ashp. No mention on the detailed tech pdf of any levels/ charts of dB of anything but the fan unit outside, which isn’t a problem in comparison.

[SteamyTea]

1 hour ago, SteveB said:

I wasn't thinking so much of using it to replace my convetional heating (which has got a smart control), more of maximising the heat recoved from the exiting air. If you take the warm air exiting and have an air to air heat pump surely that is more efficient than the MVHR heat exchanger.  And I guess it may be possible to use it for cooling in the summer.

 

I think the scaling does not optimise too well.

Generally, when it comes to any energy production, bigger is better.

[Thedreamer]

2 hours ago, SteveB said:

I wasn't thinking so much of using it to replace my convetional heating (which has got a smart control), more of maximising the heat recoved from the exiting air. If you take the warm air exiting and have an air to air heat pump surely that is more efficient than the MVHR heat exchanger.  And I guess it may be possible to use it for cooling in the summer.

 

 

I fitted a joule aero cylinder, pulls air from bathroom, ensuite and utility.

 

I'm really pleased with the results, at moment it is extremely efficient. Currently all our energy usage for the house is 10kw per day for a family of four.

 

This does a 260 litre tank for our hot water and cost £2,500 to buy.

 

Our house is a new self build with reasonable insulation and large amount of south facing glazing.

[SteamyTea]

1 hour ago, Thedreamer said:

Currently all our energy usage for the house is 10kw per day for a family of four.

 

This does a 260 litre tank for our hot water and cost £2,500 to buy.

I use about 4.5 kWh/day for everything.

 

That £2500 would buy me around 23 years of DHW.

 

This is the dilemma I have, energy is just too cheap for me to change anything.

[Thedreamer]

56 minutes ago, SteamyTea said:

I use about 4.5 kWh/day for everything.

 

That £2500 would buy me around 23 years of DHW.

 

This is the dilemma I have, energy is just too cheap for me to change anything.

 

That 4.5kWh, is that just for you?

 

The 10kWh is all our household energy for two adults and two children.

 

What's the set-up for your hot water and initial investment?

[SteamyTea]

13 minutes ago, Thedreamer said:

That 4.5kWh, is that just for you?

 

The 10kWh is all our household energy for two adults and two children.

 

What's the set-up for your hot water and initial investment?

Yes.

When I had a lodger, and once I had trained her to take a shower that was only a few minutes, my usage was not much higher.

 

One thing about putting extra people in a house is that fixed loads do not increase, so there is only a marginal increase in usage.

 

I use a basic vented, 200 lt cylinder with E7 heating.  I had to buy a new cylinder a couple of years back, cost £220, or £7/year, as it lasted 28 years.

I don't know how much it would cost to fit in a new build, I suspect it is about the cheapest installation one can do.

 

I have added extra insulation to the cupboard it is fitted to, just some sheets of PU and voids stuffed with mineral wool.  This over halved the losses.  I also run it at a relatively low 45°C or so (not checked the actual temperature, but have turned it down from the 50°C I used for years).

 

If I have guests, I can easily turn the temp up, or use the upper element, so never had a problem of lack of hot water (since I trained my old lodger).

 

If I am costing out a system, I always compare it to what I have, as I know the costs of what I use as I have been monitoring for a decade.