HVAC

__HVAC and Energy Modeling__

= = = = =Overview: =
 * HVAC** stands for Heating, Ventilation, and Air Conditioning.

Roughly estimating, we will need about 30,000 btu of heating/cooling capacity, (assumption: 12,000 btu per 400 square feet). This depends, however, on our passive heating/cooling systems, how many windows we have, and what kind of insulation). The HVAC system will consist of three components: Minisplits, ERV, and supplemental heating for very cold days.

Impact for design: we could put one mini split in each mod and an ERV between the two.

First component: minisplits.
Minisplits are a type of heating/cooling device. The minisplit consists of two parts: one which goes on the inside of the house and is mounted on the wall or ceiling, called the “handler.” The second part, the “condenser” is mounted outside the house. The air handler and the condenser are connected by an insulated tube. Because a minisplit doesn't use ducts, it is very efficient. A single unit can be placed anywhere in a room that has an exterior wall. Minisplits can come in single-zone (one air handler connected to one condenser) or multi-zone (multiple air handlers connected to one condenser).

A great resource for looking for heating and air conditioning units is[| http://thermospace.com/]. One manufacturer to look at is Mitsubishi, which produces some of the most efficient minisplit systems available. (See: __http://middleburyresearch.wikispaces.com/Mitsubishi+Mini-Split__ ). Specifically, the product line being considered is called “Mr. Slim” which comes in units of varying btu capacity. Email me (Max Bacharach) if you want more specific product numbers.

This is a picture of possible minisplit placement.

The main drawback of minisplits is that at very cold temperatures, they become less efficient and produce less heat. For example, a mini spit which produces 10,900 btu of heat when it's 47F outside might only produce 6,700 btu of heat at 17 degrees F. This may not be a problem in the private space, since the bedrooms are small enough that even a reduced-capacity minisplit system can do the job, but it will be a problem in the larger public space. This means we will need to either over-install cooling capacity in order to reach sufficient heating capacity on cold days, or we will need a supplemental heating system. What this means for design: maximize insulation to minimize loads on these systems.

Second component: supplemental heating system.
Because the minisplits probably won't supply enough heat on very cold winter days we will need a heat “booster.” There are many possibilities here:

**(a) Electric radiant floors** – these typically consist of cables built into the floor. Systems that feature mats of electrically conductive plastic are also available, and are mounted onto the subfloor below a floor covering such as tile. Electric radiant floors are usually cost-effective only if they include a significant thermal mass, such as a concrete floor. Electric radiant floors can heat up quickly and turn off when people are not in the room, improving efficiency. However, radiant flooring has heat distribution problems – the heat doesn't spread around the room well unless people are walking around. An example of radiant flooring can be found in the Maryland 2009 LEAFHouse.

**(b) Hot water (Hydronic) radiant floors** – usually more cost-effective than electric radiant floors. Water is heated by the sun and is pumped slowly through tubes in the floor. Along these lines, we could also use a capillary-based heating system installed in the floor and walls. One example is the Clina BIONIK capillary system. It is a good example of biomimicry and worth seriously looking into.

**(c) Passive heating via a thermal mass** – with high house insulation and the right type of (south facing) windows, we could place an appropriately-sized slab of concrete strategically in the home so as balance temperatures. South-facing glass lets light in, which hits the thermal mass, heating it up. Later, the thermal mass slowly releases heat. The trick is finding the right size thermal mass – if it's too big, it will absorb and release heat too slowly, and if it's too small it will do it too quickly. Unfortunately, high-thermal mass materials like brick and concrete tend to be heavy. Hence, we might want to put them in only after returning the house to Middlebury. Also, strategically-placed shades and overhangs are essential to passively heat effectively.

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Conclusion: the degree to which we will need a supplemental “booster” heating system for very cold days will depend on better heat load estimates than the ones we have now. In fact, it is likely that we will need a supplemental heating system only in the public space, not in the private space. That's why we need the help of consultant Karen Walkerman to help us learn how to use energy-modeling software.

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Third component: ERV (energy recovery ventilation).
<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">An ERV is a device to exchange inside air and outside air. The difference between an ERV and an open window is that the ERV actively works to minimize heat and energy loss because it takes the heat from the outgoing air and puts it into the incoming fresh air (or vice-versa). That way, you don't have to heat the incoming air so much in the winter (or cool the incoming air so much in the summer). <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Our ERV needs to have 40cfm capacity. (The leading HVAC engineering group, ASHRAE, recommends a minimum ventilation rate of 7.5cfm (cubic feet per minute) per occupant plus 1 cfm for every 100 square feet of occupiable floor area.) Possibly position the ERV east-west across the ceiling space of both mods.

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">One ERV to look at is Zehnder America's ComfoAir 200 ventilation system (see <span style="background-color: transparent; color: #1155cc; font-family: Arial; font-size: 15px; vertical-align: baseline;">[|__http://www.zehnderamerica.com/products/comfounit_home.asp__] <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">). It is one of the most energy-efficient ERVs on the market. However, since its capacity is 125cfm, and we only need 40cfm, it may be worthwhile to try to find a smaller ERV.

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Addendum: Liquid Desiccant Wall.
<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">The scoring for the comfort zone competition this year are different from past competitions in that there is no longer a lower bound for acceptable humidity levels. We need only keep relative indoor humidity below 60%. Moreover, given the cooking competition, which requires us to vaporize 5lbs of water in two hours, it is important that we be able to deal with abrupt spikes in indoor humidity. One solution would be to install a Liquid Desiccant Waterfall (LDW) to regulate humidity. “Liquid desiccant” just means saltwater, and it functions to draw water out of the air, thereby reducing indoor humidity. Liquid Desiccant Waterfalls were used successfully by the University of Maryland in 2007 and 2011 (see <span style="background-color: transparent; color: #1155cc; font-family: Arial; font-size: 15px; vertical-align: baseline;">[|__http://2007.solarteam.org/page.php?id=641__] <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;"> and <span style="background-color: transparent; color: #1155cc; font-family: Arial; font-size: 15px; vertical-align: baseline;">[|__http://2011.solarteam.org/__] <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">). An LDW could either be hidden behind a wall, or it could be visible like the waterfall in the Axinn Starr building. From the perspective of homeowner comfort, the sound of running water makes people feel cooler when it is very hot. In addition, by efficiently reducing the humidity of the indoor air, an LDW would reduce the cost of air conditioning. I haven't done so much research on this, but a solar-powered LDW seems very promising.

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">The relevant rules are:

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 13px; text-decoration: none; vertical-align: baseline;">8-4. Desiccant Systems <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 13px; text-decoration: none; vertical-align: baseline;">If a desiccant system is used, it must be regenerative. <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 13px; text-decoration: none; vertical-align: baseline;">(Draft Rules, Page 14)
 * 1) <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 13px; text-decoration: none; vertical-align: baseline;">To ensure that the desiccant has been fully regenerated by the conclusion of the Energy Balance Contest, the desiccant material or device must be easily measurable.
 * 2) <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 13px; text-decoration: none; vertical-align: baseline;">In most cases, the material or device will be measured prior to and at the conclusion of the Energy Balance Contest. In some cases, a measurement at the conclusion of the Energy Balance Contest may not be necessary.
 * 3) <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 13px; text-decoration: none; vertical-align: baseline;">At the conclusion of the Energy Balance Contest, the weight of the desiccant material or device shall be less than or equal to its initial weight.
 * 4) <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 13px; text-decoration: none; vertical-align: baseline;">Some desiccant systems with very low moisture storage capacities may be exempt from this requirement. Exemptions will be granted on a case-by-case basis by the competition manager.

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Looking ahead:
<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Whatever systems we use for HVAC, they need to be integrated if we are to maximize their potential efficiency. In the past, teams have used user-friendly devices, like an iPad or other touch-screen display, to make a user-friendly interface for the homeowner. The interface should be “smart.” It needs to be integrated with the electrical system, allowing the homeowners both control as well as the ability to see how much electricity they use and where. Other ideas for a smart system may involve the use of (infrared?) sensors that automatically activate temperature controls in specific spaces when there are people in those spaces, and automatically deactivate them when people leave the house. Another possibility for a smart system would be to have the computer system track weather predictions and prepare for future weather conditions ahead of time. Someone with computer skills could have a lot of fun with this.

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Finally, HVAC success will require energy modeling skills. That means at least one or two team members will need to learn how to use complex (and extremely powerful) energy modeling software to calculate heat load requirements. To assist in the process, we have contacted Ms. Karen Walkerman, an energy modeling consultant. She is based in Burlington and is willing to meet with us (see below)

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Contacts:
<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Ms. Karen Walkerman is an energy modeling consultant. She would be delighted to help us.

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Karen Walkerman <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Second Law <span style="background-color: transparent; color: #000080; font-family: Arial; font-size: 15px; vertical-align: baseline;">__802-238-0980__ <span style="background-color: transparent; color: #000080; font-family: Arial; font-size: 15px; vertical-align: baseline;">__karen@secondlaw.biz__

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 15px; text-decoration: none; vertical-align: baseline;">Interested people on the team included Pat Li, Nick Bachmann, Joseph Mutter, Max Bacharach (me), and Jun Chen.

Other Information
An authoritative resource for anyone researching this might be the first chapter of the ASHRAE 2011 HVAC Handbook.

[] Santa Clara 2007 Team used a really cool water based cooling system

One of the Standards for Heating and cooling in SD Mitsubishi Mini-Splits Mitsubishi Mini-Split

HRV vs. ERV ventilation systems