Thermodynamics of Outdoor Hotel Patio

[Matchstick]

What are best methods to maximize heat retention in design and furnishings for a 8,000 square foot outdoor hotel patio.

 

 

 

We'll start with forced air heat under the entire wood framed patio, gas/electric/infrared heaters mounted on walls and ceilings, select metal and stone based furniture and fixtures for heat retention, plus overhead canopies/umbrellas, firepits, etc.

 

What else should we consider (besides sweaters) to keep people warm in an outdoor environment?

 

 

 

 

[Phi for All]

What are your temperature ranges, daytime and nighttime? Is this for year round use or just certain seasons? What about wind?

 

"... forced air heat under the entire wood framed patio"? Is this vented out to the patio area or is the floor heated from below using the forced air heat from the room underneath?

 

This may be more of an engineering thread. If it starts to head that way I may move it so you'll get more qualified attention.

[Matchstick]

Thanks!

Temp in So Cal ranges 45-70 during off season PM October-May. Intent is for year round use. Location is harbor waterfront so wind cab be an issue; a 4' glass wall facing the water perimeter is intended to mitigate. Floor heating will be vented out to the patio area which sits on thick concrete slab.

 

 

[michel123456]

Can't you cover your patio in winter time?

[Matchstick]

Funny you say that.

We are thinking of incorporating a steel rib beam structure that a fabric of some sort could be rolled out as temp cover - expensive but a possibility.

 

 

We do plan on having 10-15 cabanas (with heaters) along the perimeter of the patio which will surround an above ground pool and spa.

Plus there will be a 10-12 foot overhang (lattice with poly top, canvass or roof structure TBD) from the current building to cover a portion of the dining area, with clear marine isinglass roll down walls.

 

The question is whether we can mitigate the chill in the balance of the area of about 5,000 SF with other methods to avoid a roof.

 

 

[michel123456]

You have a lot of solutions for a retractable roof

_glass (expensive & heavy structure.

_fabric, low cost but not very much reliable.

_polycarbonate sheets.

_PVC membrane on aluminium structure.

_up-to-date ETFE inflated membrane. http://www.vector-foiltec.com/en/projects/application/roof-moveable.html

 

 

If there is a pool in your atrium it will be difficult to manage acceptable conditions under the same roof with other functions like restaurant for example or even sitting area. Temperature & humidity will not be compatible.

 

So, if you want no roof at all, I would suggest radiation heating.

And metallic furniture is not a good idea IMHO. Generally speaking it would be preferable for the guests to touch material with low thermal conductivity.

[Matchstick]

Great idea!

This retractable roof idea could do the trick.

Basically a series of semi-clear PVC panels on an "flowing" aluminum structure.

Rolls out garage door style from a "stacked" group of panels accordion-like from a rectangular box.

The semi-clear PVC helps admit the heat during the day.

We could even make an alternate series of panels with canvas or sail material.

The structure looks like a wave - unique and appealing open, with a material set of panels or with the PVC "glass" panels.

One or both sides could draped to hold the heat in.

It could even be installed with minor "tilts" so that rain would collect in just 2 or 3 "dip" sections of the wave structure

 

 

For furnishings and fixtures are there colors, surfaces, forms or other considerations (plants) that would be advisable to maintain/retain the greatest amount of heat generated from the sub-floor vents and/or the PVC "roof"?

 

Did you suggest that the humidity from a heated pool and spa should not be considered helpful and in fact would be incompatible if contained by a roof structure and "shared" with conditions required for a nearby restaurant?

 

 

[Externet]

Hi.

I believe what has to be observed is, in which way the heat would be lost and attack that.

 

In your heated pool patio, I would say the lack of a roof would be the largest route for the heat to escape as warmer air always will immediately rise. The problem is that volume of escaping warm air is being replaced with cold air. If the pool water is kept colder than the desired air temperature the water can be a huge heat sink too.

 

For a no-roof condition, it would be worth checking what aerodynamics engineering can contribute with to reduce the losses. Those overhead vertical 'air knife' fanned doors at a walk-in freezer do a decent work rejecting warm air to enter where it is unwanted.

Not to suggest installation of such slit fans on top of the perimeter; but to implement some architectural funneling elements at the fencing top that can use the incoming wind to create vortexes or a horizontal knife effect to separate the warmed area from escaping upwards with ease.

[Matchstick]

Another great idea!

We had considered using tensile fabric structures as a way to frame the space, and also to give it a "sail" looking sculptural feeling to the space.

Should we build these then it would be prudent to create them (or some) with a convex shape and a downward glance and equip a low noise "air knife" to funnel hot air such that it deflects to heat a portion of the patio.

The pool water will be always heated to a level hotter then air temp so that should help a bit.

[michel123456]

Did you suggest that the humidity from a heated pool and spa should not be considered helpful and in fact would be incompatible if contained by a roof structure and "shared" with conditions required for a nearby restaurant?

Exactly.

[CaptainPanic]

How to reduce expenses:

- close off the patio

- remove the pool

- heat with gas instead of electricity.

 

I'll elaborate a bit:

 

Get a roof. Don't be shy to spend some money on that roof, it will pay itself back in energy savings (yes, even the expensive roofs will have a payback - expensive glass roofs will close off better, and save more energy). Just do a quick calculation of your energy bill for an open patio (basically all heating at max. power) and realize that you can reduce that by 90% (maybe more ) if you close it off. Also close off the sides. Hot air that escapes is by far your greatest loss of energy... so keep that hot air inside.

 

The pool will only cost energy... it will not be an energy saver at all. You need to heat the water... and then the water evaporates (and your energy is gone - it does not get transferred into the air! It is used to evaporate the water!). Regardless of whether you have a roof or not, the pool will cost money and you gain nothing at all, except that it looks nice... I discuss only the energy here, not aesthetics.

 

Gas is generally at least twice as cheap per unit of energy as electricity. This, of course, also depends a lot on where you live. In Western Europe, gas is cheaper than electricity by up to a factor 3.

[michel123456]

Gas is generally at least twice as cheap per unit of energy as electricity. This, of course, also depends a lot on where you live. In Western Europe, gas is cheaper than electricity by up to a factor 3.

 

That is a good basis for discussion.

Physically speaking, electricity is the most uneffective way for heating. Generally, electricity is produced from fuel or gas that heats water, producing vapor in a turbine with IIRC more than 50% energetic loss, then transmit through wires (other loss), then retransformed in heat (another loss). The whole process is dumb: why not use gas or fuel directly to produce heat where you need it. So under this POV Captain is right.

Things change when electricity production does not depend on fossil fuels but on renewable energy, wind or solar. In this case you care much less about energy losses and electric heating becomes green.

If electricity comes fron nuclear source, the question whether it is green or not is still open.

All this not regarding the cost.

 

This article about efficiency.

Edited October 24, 2011 by michel123456

[Matchstick]

Thanks for the insights! We will incorporate a roof for about 2,000 SF of the patio area to cover the dining room. Depending on costs we might add a gazebo for additional partial coverage (covering all 5,000+ SF does get costly if it's a quality architectural solution like a fabric structure which runs $125/FT). So at this point we are looking to mitigate the cold air in the open section with a combination of heating solutions, including: electric heaters in cabanas, gas fire pits on the deck (some with upwards of 80,000 BTU's) and gas heat lamps. For under the deck we're looking at Hydronic Heating which has efficiency benefits: http://www.hydronicheating.net/. The pool is an integral part of the amenities and with it's glass side, a dramatic focal point of the patio - so have to keep that.

[michel123456]

For under the deck we're looking at Hydronic Heating which has efficiency benefits:

 

Is it for use under a wooden deck? Exterior? If yes it is not exactly adequate IMHO.

[Matchstick]

Yes, wooden deck exterior, most of it 18-24" off the concrete slab. Which of the heating choices I wonder is most adequate (cost/efficiency): radiant (Hydronic), forced air, or?

[michel123456]

Yes, wooden deck exterior, most of it 18-24" off the concrete slab. Which of the heating choices I wonder is most adequate (cost/efficiency): radiant (Hydronic), forced air, or?

 

I don't get it, is that 60 cm above the concrete slab? with open joints?

[Matchstick]

Yes, higher or lower depending on heating system.

[CaptainPanic]

Thanks for the insights! We will incorporate a roof for about 2,000 SF of the patio area to cover the dining room. Depending on costs we might add a gazebo for additional partial coverage (covering all 5,000+ SF does get costly if it's a quality architectural solution like a fabric structure which runs $125/FT). So at this point we are looking to mitigate the cold air in the open section with a combination of heating solutions, including: electric heaters in cabanas, gas fire pits on the deck (some with upwards of 80,000 BTU's) and gas heat lamps. For under the deck we're looking at Hydronic Heating which has efficiency benefits: http://www.hydronicheating.net/. The pool is an integral part of the amenities and with it's glass side, a dramatic focal point of the patio - so have to keep that.

I do not think you're making the right decision, and I think you're wasting money... but I think you do not understand how expensive heating can be, so I will see if I can explain the basics first.

 

80,000 BTU is the equivalent of about 70-80 sqft of natural gas, or for example about 4 kg of wood. I guess that is what a single heater will use in 1 day. How many such heaters do you have? Depending on the gas prices where you are, one single heater will burn up around $1 - $2 per day. Depending how many days you heat, this can go up to $50 - $600 per year... and that's just for 1 heater.

 

Do you know how much you spend to heat the whole place every day?

 

You really need to make a good estimate of the costs of the energy (for the next couple of years!) before you can conclude that a roof is too expensive!!!!

[michel123456]

I suppose the heting system is not supposed to be used to whole year round. What are the weather conditions in the area?

 

In my mediterranean country, exterior spaces are sometimes heated by radiation (simple or impressive like this one) but only in several urban places where there is no substantial room inside. In resort hotels that are closed during the winter, no heating system exist in exterior areas at all, because during low season there are also less tourists and they all fill inside.

You must first take a serious look at the probability of occupation of your exterior area before engaging into high cost installation.

 

As for the deck, you must know that wood is an excellent insulator, and a very bad radiant. It is not a good material to use with floor heating. If you really want to use wood, I would suggest to find another heating solution. If you are sure the heating system is most adequate, you could replace wood with ceramics. There are excellent tiles that mimic wood, dimension about 15 cm wide & 90 cm long, from many providers.

Edited October 25, 2011 by michel123456