Air Source Heat Pump - Cylinder Design Concept

[MickD]

Hi All,

 

I am in the last stage of completing on a house,  So I have started the design of electrics, audio visual, and Lutron lighting throughout.

 

The issue I am having is I don't know much about MVHR and ventilation,  I have done lots of reading but wanted to ask an expert that could guide / critic my idea.

 

Design Features:

• Dimplex Air Source Heat Pump Cylinder
• Use the warm air from the Lutron and AV Rack to help heat the hot water.
• Connect the MVHR to the AV rack cupboard,  to utilise the heat recovery when the cylinder is not running.
• 150mm pipe from the Cylinder to the AV rack top part (heat rises)
• 150mm Pipe from outside to the AV rack to allow cool air to be pulled in and cool down the equipment.
• AV / Lutron Rack to be sealed in using rubber,  and the whole cupboard the rack sits inside to be completely air sealed.
• MVHR Pipe will have a 75mm Solenoid valve that connects to the Fan cable of the Air Source Heat Pump - when the fan is running the normally open solenoid will close.

 

I have created a drawing,  of the proposed system which will explain my idea...

 

So what do you think,  and thank you for your time.

 

Mick

 

[Jeremy Harris]

Welcome,

 

First point is what level of airtightness have you managed to achieve?

 

Unless you've sealed up the house to better than around 3 ACH at 50 Pa it's pretty doubtful as to whether MVHR would be worth installing.  Ideally, MVHR really need the airtightness to be better than about 1 ACH to reap significant benefits.  This is a tough target to achieve; few houses built to current building regs will be this airtight.

 

If the lighting system is so inefficient as give off lots of heat, then I think the first thing to do would be to change it for something less wasteful, as that would be both cheaper and more effective than trying to recover heat from an inefficient lighting system.

[MickD]

The Lighting is very efficient compared normal lighting in a house,  its a control system,  I trim all lighting down to 80% at maximum this has a 20% saving on every light output in the house.

Lights are automatically turned off if no activity in rooms after 1 hour,  where a normal switch needs an operator to remember it needs switching off.

 

I design high end lighting systems as a job.

 

I put the lighting in the same cupboard as the AV rack because I want to use the heat to help heat the house,  its the AV that gives off heat  (AV = audio visual) this includes amps and HDBaseT matrixes for the whole house television and music distribution,  I have a Atmos setup and the amp runs 11 speakers and 2 sub woofers. these amps get very warm...

 

Also none of this is set in stone yet,  I have not completed on the purchase (I get keys in a week) and it can be changed,  this is why I am asking.

 

We are also lining all internal walls with 50mm + 12 Insulated plasterboard.  And early next year the whole house from the outside is having 100mm of insulation installed,  I expect the house to be very air tight.

 

Thank you very much for your input

 

 

Edited August 30, 2019 by MickD

[Jeremy Harris]

If the lighting is efficient, then there won't be any significant heat to recover from the control cabinet, so it wouldn't be worth the effort of trying to recover wasted energy from it. 

 

As an example, our 130m² house has a total lighting power input, with all lights on, of less than 250 W.  I'd expect any switching system to be at least 95% efficient, so that means that, with all the lights on, the wasted energy in the switches/control system would be around  12.5 W.  Apart from this heat loss being very low, it ends up directly heating the house, so there is no real merit in trying to pass this through the MVHR.

[MickD]

37 minutes ago, JSHarris said:

If the lighting is efficient, then there won't be any significant heat to recover from the control cabinet, so it wouldn't be worth the effort of trying to recover wasted energy from it. 

 

Thank you for the reply,  It's not the lighting its the AV (Audio Visual Rack) I think I might have confused you mentioning lighting.

 

Our AV rack contains the following:

 

1 x Marrantz Dolby Atmos Amp (this is for my cinema room surround sound) these get very very warm as they drive 11 speakers and subwoofer.

1 x Marrantz 5.1 Amplifier (this is for our dining room media room) also gets very warm 6 speakers

1 x Marrantz 5.1 amplifier (this is for my master bedroom surround sound) again very warm 6 speakers

1 x Wyrestorm 4K HDbaseT Matrix,  this distributes HD from the rack to all the televisions (very warm)

2 x Sky HD boxes. (quite warm)

3 x Apple TV (not really much these are good)

6 x Sonos Connects (slightly warm)

1 x Sonance 4 Channel DSP amplifier (runs music for all other zones) drives 10 speakers.

2 x Sonace DSP amplifiers (these run my 2 subwoofers in the cinema room) (quite warm)

1 x savant processor (slightly warm)

1 x 2u Rack mount PC server that runs flex and all our files (pictures etc) this is a 400w PSU power server - runs quite warm.

1 x Draytek Managed network switch P2880 (quite warm)

1 x Ruckus Wifi Zone Manager

1 x Draytek Router 

 

as you can see there is tons of heat coming off our Audio Visual systems that we have.  and reusing this heat is what I am trying to do.

 

I do have to mention,  that the cylinder is nothing to do with MVHR its for the hot water,  I wanted to use the heat to help with two things

 

1. Cool down the rack equipment,  and prolong equipment life
2. Use the Excess Heat to help with the MVHR,  and also heat the hot water when its called for.

Hope that explains it better.

 

Mick

 

 

Edited August 30, 2019 by MickD

[Jeremy Harris]

The key thing is that the waste heat from the rack isn't really wasted, as it ends up inside the thermal envelope, so contributes to keeping the house warm.  In effect, it just offsets the heating requirement, so is a direct, 1:1, saving from the heating bill.  If the rack is so inefficient that it creates lots of waste heat, then adding forced air cooling from the room would help both cool it, and distribute heat to the house.

 

It all hinges on efficiency,  and I find it hard to believe that even a big house audio visual system would be so inefficient as to generate a useful amount of heat from the control/amplification rack.  A pretty loud audio system is only going to deliver maybe 5 to 10 W of acoustic power into an average sized room (even that is probably up in the region where damage to hearing is likely). Even a crappy class A amplifier is only going to draw around 100 W to deliver that acoustic power level, a more common class C/B amp would draw maybe 30 W, and a decent class D might be less than 15 W.  Of course, the peak power ratings will be a great deal higher, but the peak-to-mean ratio in music is pretty high, and it's the mean power that ends up determining the heat loss through inefficiency.

 

Lightin system switching should be virtually lossless, so there will be near-zero heat recovery from the lighting control side of the system.

[MickD]

1 minute ago, JSHarris said:

The key thing is that the waste heat from the rack isn't really wasted, as it ends up inside the thermal envelope, so contributes to keeping the house warm.  In effect, it just offsets the heating requirement, so is a direct, 1:1, saving from the heating bill.  If the rack is so inefficient that it creates lots of waste heat, then adding forced air cooling from the room would help both cool it, and distribute heat to the house.

 

Thank you very much for this,  the main concept is cooling the equipment but I wanted to make sure my design would work (see my original drawing).

 

AV Receiver Amps today don't just provide sound they also send HD signals and receive HD signals these amps are around 3-4u in size each so they are very big amps and do soo much more than play music they drive a whole cinema room sound and vision and media room alike. (the SR7013 has 9 power amps inside the  1 amp :))

 

Take a HD sky box for example, for something that just puts a signal on the tv they get very warm and draw 19w in standby.

 

Mick

 

 

 

 

 

 

 

 

[Jeremy Harris]

I appreciate what you're saying, but the heat produced is directly proportional to efficiency, and the standby power of domestic equipment has to comply with current regulations, so can never be anywhere near 19 W (check the current regs on this if you don't believe me).  Older kit could consume a few watts on standby, but not anything sold in the past few years, as there has been a gradual clamp down on standby power consumption of all domestic kit.

 

The size of the amps has little to do with their heat output, as in a domestic environment they just cannot deliver a high mean power output.  For example, a decent sound system in a room of around 5m x 5m, will deliver an ear-splitting SPL with about 10W of audio power, so maybe 100 W of electrical power, and 90 W of wasted heat, with a poor efficiency class A amp.  With a decent class D there may well only be around 5 W of wasted heat, not enough to bother about doing anything with, when you consider that an immersion heater is typically around 3,000 W.

[MickD]

I think we are digressing a little,  I don't have a problem paying my bill or what the costs are,  but all AV racks generate quite allot of heat because they allow you to consolidate all your equipment in one place,  we don't need to have regs to know that putting 30 pieces of equipment that would normally be spread across the home in once place will generate heat.

 

My current cupboard hits around 35-40c and then the extractor fan kicks in... (very inefficient pumping it out the house).

 

I am trying to find out if my design will help with cooling the equipment and also use the inefficient heat generated in an efficient way by helping to heat the home and also heat the hot water.

 

EDIT I should mention: I have two pieces of equipment going in 

 

1. Air Source Heat Pump Cylinder - this is for hot water has a heat pump built in the top of the cylinder
2. Vent Axia - MVHR

 

But more importantly I was after finding out if the design works,  there is solenoid valves,  sealed cabinets,  I need to know if the design in the way the heat recovery will operate in the AV cupboard.  I will be running a 150mm duct from outside air to the cupboard as I am nervous to create a vacuum in the utility room this is going to sit in.

 

But I do appreciate all your comments they are very informative!

 

Mick

 

 

Edited August 30, 2019 by MickD

[Jeremy Harris]

Sorry, I didn't mean to imply anything about bills, it's solely the laws of physics and the true amount of heat that is available from any bit of kit that is delivering a service to the house, that's all.

 

It's a hard fact that any lighting control system isn't going to generate a lot of heat, if it does then it needs sorting, as there is no need for any such control system to waste more than a tiny proportion of the power of the controlled lighting.  The same goes for audio, or video.  Audio  amps shouldn't be that inefficient that they generate significant amounts of heat, in the context of a domestic environment, and safe levels of SPL. 

 

There's just a massive disparity between the likely waste heat from even a really comprehensive domestic audio/visual system and the typical heating/hot water requirement.  This makes it really hard to justify spending any significant amount on heat recovery from this low level waste heat, as the probability is that the capital cost of the system will be orders of magnitude more costly than the true value of any recovered useful heat.

[MickD]

gotcha

 

 

[Nickfromwales]

Hi @MickD

Your hot water unit ( if I have the principal correct ) utilises Exhaust Air Heat Recovery, so is reliant on heat from the whole house. Just vent the heated air from the AV cupbaord directly into the space immediately outside the cupboard and the heat will be recovered regardless. 

I'd be very worried about having so much air flow through my sensitive electronics, when the solenoid closes, as that would promote the influx of dust  etc in much higher concentrations as opposed to just convection ventilating the equipment via high and low ventilation 'grilles'.  Look how much crap builds up on the back of even a slimline TV without such positive channelling of all the dust etc directly past it .  

Put a coupe of air movers  ( 2 x 100mm Papst fans ) in the lower opening and just get a bit of airflow to stop stagnation of the heat, and leave the MVHR and EAHR to work their magic without any intervention.

I'm old school and still run a Yamaha DSP A2, but bloody hell it throws some power out!! Was running Kef 104.2's until the neighbours moaned so now run Q65's  It's not the same.......

[SteamyTea]

What may seem like a lot of heat may not be.

Air takes 1 J.kg^-1.K^-1 to heat.

So a relatively small cupboard may seem to be warm, but it has not taken much energy yo heat it up.

All my lighting, if I left it on, draws 30W, I hate leaving lights on, but in the scheme of things, it is 100^th of what my kettle draws.

Edited August 30, 2019 by SteamyTea

[MickD]

9 hours ago, Nickfromwales said:

Hi @MickD

Your hot water unit ( if I have the principal correct ) utilises Exhaust Air Heat Recovery, so is reliant on heat from the whole house.

 

 

 Hi Nick,

Thank you for your reply.

Correct, the cylinder is a EAHR.

 

9 hours ago, Nickfromwales said:

Just vent the heated air from the AV cupbaord directly into the space immediately outside the cupboard and the heat will be recovered regardless. 

I'd be very worried about having so much air flow through my sensitive electronics, when the solenoid closes, as that would promote the influx of dust  etc in much higher concentrations as opposed to just convection ventilating the equipment via high and low ventilation 'grilles'.  Look how much crap builds up on the back of even a slimline TV without such positive channelling of all the dust etc directly past it .  

 

 

This is exactly the kind of information I am after,  Dust, bugs, and the effect on the equipment for the high velocity air flow.

 

Playing devils advocate the Cylinder has a cold to 60c time of around 4-6 hours at 23c (12 hours at -5) without immersion just using the EAHR.  And this is generally only after holidays and on initial startup.

I called Dimplex and they told me depending on the exhaust temperature,  top up is usually only a few minutes up to 15 minutes at -5 degrees (this is not in the manual, this was a direct discussion with technical). being honest I don't know how often top up will occur - maybe another call to technical lol...

 

I completely get the high velocity of air flow in the AV rack and around the components,  and as you said dust is the biggest worry as dust and electronics are a no no.

Because of the general short bursts of velocity Air intake would it still be so bad. most of the time the MVHR will be taking the heat at a much lower velocity (which I don't know yet).

 

9 hours ago, Nickfromwales said:

I'm old school and still run a Yamaha DSP A2, but bloody hell it throws some power out!! Was running Kef 104.2's until the neighbours moaned so now run Q65's  It's not the same.......

 

The Yamaha A2 is a fantastic amp with awesome sound and the KEFs are a much better fit,  got to keep the neighbours happy!

 

My SR7013 AV amp gets so hot you can just about touch it...  its just the nature of the beasts!

 

Thank you very much for the reply.

[MickD]

9 hours ago, SteamyTea said:

What may seem like a lot of heat may not be.

Air takes 1 J.kg^-1.K^-1 to heat.

So a relatively small cupboard may seem to be warm, but it has not taken much energy yo heat it up.

All my lighting, if I left it on, draws 30W, I hate leaving lights on, but in the scheme of things, it is 100^th of what my kettle draws.

 

this is another great point,  the heat build up that I have in my current rack (35C-40C) I'm guessing is a build up of the heat over a time,  and with effective extraction this would therefor be much less heat because its not stale air in the cupboard.

 

correct me if wrong - which would also mean the cupboard with effective air flow would not do much for heating because its a very small amount being actually generated by the equipment,  just feels like allot because of the buildup happening over time.

 

Thank you

[SteamyTea]

6 minutes ago, MickD said:

just feels like allot because of the buildup happening over time.

Yes.

You can work it out, find the volume of the cupboard, multiple by the density of air, work out how many joules is being pumped into it and you will end up with the rise in temperature.

[Jeremy Harris]

A quick look at how much air needs to be shifted to be able to extract a given amount of heat might be useful.  The heat capacity of air is as @SteamyTea says, about 1 J⋅g⁻¹⋅K⁻¹, and the heat capacity of water is about  4.18 J⋅g⁻¹⋅K⁻¹, so if you want to heat, say, 200 litres of water from an incoming cold water temperature of 8°C to a hot tank temperature of 60°C, then you need about 43.472 MJ of heat energy.  Ignoring the small heat input from the compressor in the heat pump, this means that the air flowing into it has to have around this much heat energy.  Working backwards, using the heat capacity of air, and assuming that the air intake to the heat pump is 25°C and the exhaust is ~0°C (pretty typical for an EAHP) then you need to pump about 1,400m³ of air through it in order to heat the tank.  You can easily work out how much air flow you can get through your cabinet and what that is likely to contribute.  A pretty high air flow rate of, say, 10l/m, with a tank heating time of, say, 4 hours, would mean that the cabinet contributed about 2.4m³ out of the ~1,400m³ that the EAHP needs, or a bit under 0.2%.

 

[SteamyTea]

3 minutes ago, JSHarris said:

or a bit under 0.2%.

It goes back to the old story about the Cornishmen that were really cold.

So they sat around a candle to warm up.

One asked what they would do if they got really really cold.

To which the reply was.

'Light the candle'.

[MickD]

I am also thinking about the adjustment in air temperatures because of the cabinet and flow through the warm house...

 

Would there be any,  I get that it will contribute 0.2%,  but because of the input fromqoutside running through a cabinet inside would there not be an increase in air temperature?

 

Lets say outside was 10c but because the air moving through the house into the cupboard and then into the exhaust intake at the top would there be no increase in temperature that is useful to the AEHR ?  there is massive difference in heating times based on AEHR temperatures.

 

 And it would keep the equipment cool which has a value massively above the MVHR and the AEHR...

 

Thanks for the replies.

 

Mick

 

 

Edited August 31, 2019 by MickD

[Nick1c]

Why not have a thermostatically controlled fan exhausting into a largish area & fit vents into the av cupboard with dust filters fitted - should keep the kit cooler & clean for not much, the heat stays in the thermal envelope. 

[MickD]

6 minutes ago, Nick1c said:

Why not have a thermostatically controlled fan exhausting into a largish area & fit vents into the av cupboard with dust filters fitted - should keep the kit cooler & clean for not much, the heat stays in the thermal envelope. 

 

So instead of ducting into the AEHR and the MVHR just have it ducting into the house then let the MVHR and AEHR do their normal thing...  as the heat will recovered anyway in the envelope of the house...

 

So just use some basic fan on a thermostat that sends it back into the house...

 

Love the idea of the filters...

 

What about the summer months I was thinking the MVHR would be on bypass mode and just chuck it out the house...

Would the house MVHR do the same also as its venting the house?

 

Thank you.

 

Mick

Edited August 31, 2019 by MickD

[SteamyTea]

59 minutes ago, MickD said:

Lets say outside was 10c but because the air moving through the house into the cupboard and then into the exhaust intake at the top would there be no increase in temperature that is useful to the AEHR ?  there is massive difference in heating times based on AEHR temperatures.

 

 And it would keep the equipment cool which has a value massively above the MVHR and the AEHR

Not sure how no increase in temperature can shorten then heating time from the AEHR.

If the equipment needs cooling, cool it with a fan, don't over complicate it.

Energy scavenging is not really worth the effort.

https://www.newscientist.com/article/2186721-green-car-tyres-can-generate-energy-while-monitoring-road-conditions/

[joth]

Thinking of the two scenarios:

- energy scavenging in winter. Just cool the equipment into the house general airspace and let the exhaust air heat pump do it's thing elsewhere. Same as the fridge/freezer or whatever. Unless the air is damp or smelly, no need to duct it straight out.

- cooling the gear while minimising house overheating in summer. This is where the ducting makes sense for me: stopping the hotter air mingling with the house saves on the expense of active cooling elsewhere. So I'm thinking to get the equipment cupboard vented directly to MVHR for this purpose in our house (but I don't have the exhaust air heat pump).

Can you "reverse" the exhaust heatpump in summer? (I.e. to use it to actively cool the house?). If so, maybe it's a wash and the same non-ducted argument works just as well in both scenarios.

 

For equipment cooling it is interesting to follow how large scale data centers  evolved. Originally they were all about active refrigeration cooling dumping cold air on top of equipment racks. These days they focus on letting as much ambient temperature air freely into the building as possible, but then very carefully capture all the hot air from every machine via a "hot aisle" and exhaust it out the other side of the building without letting it mingle with the incoming air at all. In cool temperate regions this can mean completely heat pump/refrigeration free passive cooling.

 

[Jeremy Harris]

I think I'd want to concentrate on avoiding all the wasted heat from inefficient systems first, as that makes more sense than creating a problem and then trying to fix it with a more complex installation.  There's no good reason for lighting controls to waste more than a very small amount of energy, and the same applies to modern AV gear.  It certainly was the case years ago that AV kit was pretty inefficient.  Back in the early 1970's my Linsley Hood class A power amp used around 180 W or so, all the time it was powered up.  A more modern, efficient, design can deliver the same quality with far better efficiency, wasting a great deal less energy and so needing a lot less cooling.  The same goes for things like satellite boxes.  The first Humax HDR I bought years ago wasted loads of energy, and ran pretty hot, even when in standby.  The one I bought about a year ago uses much less power than the old one,  barely gets warm when running, and is cold when in standby, has a snappier user interface and greater recording capacity.

[Ed Davies]

12 hours ago, SteamyTea said:

Air takes 1 J.kg^-1.K^-1 to heat.

 

Typo: 1 kJ·kg^-1·K^-1 (so a thousand times more).